Premium to Freemium: Adapting Rimworld to Mobile

More often than not, when you ask people to picture a mobile game, they’ll think of a role-playing game, puzzle game, strategy game, or even an action game. Rarely will they picture a simulation game, or sim.

If they do, they may not think of it as a sim game at all. A sim largely throws out specific gameplay goals, rules, stories, and challenges, instead offering ‘emergent’ gameplay: dynamic events and objectives arising from in-game actors (players, NPCs, items, etc.) acting under a standard set of complex systems. These in-game systems simulate real-world systems far more closely than non-sim games, leading to much less abstraction, and greater player agency and engagement with their in-game avatars.

There are a surprising number of successful mobile sim games, including SimCity BuildIt, Fallout Shelter, Animal Crossing: Pocket Camp, and of course The Sims. While these sims rank somewhat low in complexity among the other games in their respective IPs, and vary in the scale of their simulation, all are definitely sim games.

One of the most critically-acclaimed sims on PC is a sci-fi colony sim called Rimworld, in which you oversee a group of space travelers (pawns) stranded on an alien planet. Site SteamDB lists Rimworld as the platform’s 6th highest game of all time (link). The game currently sits at 71,905 reviews, of which 98.29% are positive (considered Overwhelmingly Positive). Per the game’s description on Steam:

A sci-fi colony sim driven by an intelligent AI storyteller. Generates stories by simulating psychology, ecology, gunplay, melee combat, climate, biomes, diplomacy, interpersonal relationships, art, medicine, trade, and more.

Much of the game’s draw lies in the interplay of its complex sim systems, such that the game describes itself as a “story generator”. As the description suggests, all resources, items, wildlife, and pawns throughout the randomly-generated game world are governed by these systems. The colony’s survival and success are largely guided by the moods, desires, and randomly generated quirks and skills of every pawn, as well as their interpersonal relationships.

Just about every other Rimworld player I’ve spoken to has fond memories and fascinating stories to tell, stories no other game could have told the same way.

What new stories might a mobile, free-to-play Rimworld offer?

Why Rimworld?

Though the game’s massive commercial and critical success on PC paints a clear picture of its potential, plenty of games see nuclear success before quickly fading into obscurity. Based on its player and streaming success since its 2016 release, that outcome seems unlikely:

Rimworld (2016) Steam Concurrent Players

Given that so much of the appeal behind platforms like Twitch is watching stories unfold alongside your favorite streamer and the community, it is hardly surprising to see Rimworld sustain steady activity on Twitch. That its streaming activity hasn’t grown much alongside its playerbase reflects a fundamental disinterest on the part of Ludeon Studios in the potential for the game’s social aspect. A mobile adaptation of Rimworld that properly leverages the game’s social appeal would be a major improvement.

One differentiating feature of Rimworld, when compared to other sims, is the challenge involved. Even on lower difficulties, the number of systems at-play can be overwhelming. Nevertheless, I have personally seen even casual gamers get hooked by the game’s open-ended nature, and play well into the night. With emergence and unpredictability being some of the game’s greatest strengths, Rimworld’s unique brand of settlement-building could be a fascinating alternative to many past and present strategy games, where every player faces an identical starting point and progression.

The success of some particular mobile games released in the past year, as described by John Brycer (link), indicates there is a massive market for games that provide unique, complex gameplay. No longer must mobile games be watered-down versions of console/PC games, or follow derivative, copy-paste formulas and progression paths. Even simply combining mobile trappings with console-level gameplay has proven to be a pathway to success, and mobile gamers are craving more high-quality mobile experiences. Rimworld, as a game already known for being approachable yet incredibly deep, may just fit the bill.

Basic Parameters

In the interest of not only preserving what has made Rimworld a success but also expanding on areas where it has unmet potential, there are four requirements that our hypothetical adaptation should meet:

• Dynamic simulated systems

Simulated systems are at the core of Rimworld’s capacity to engage players with emergent gameplay. The emergent events between in-game actors, and stories that arise from them, can stick with players for a long time: the result is positive reviews, word-of-mouth growth, and high engagement. While these systems may be simplified, and a few may be stripped away or replaced by the AI event generator, they should be preserved as much as reasonably possible.

• Persistent world and colony

The emergent gameplay and storytelling at the heart of Rimworld is made all the more impactful when the player is attached to their pawns and emotionally invested in the outcome of their gameplay actions. Over time, the player should feel pride toward their colony, and grow attached to their pawns. This effect can only be achieved with a persistent, growing colony rather than short, one-off sessions.

• World map with random events

The spatial relationships between the player and other colonies, as well as NPCs, resources, and events, help drive a feeling of connectedness with the larger game world. These relationships also affect certain in-game decisions related to caravans, trade, climate, and quests. Equally as important, they influence the random events that affect player colonies. As with the simulated systems, the world map should be preserved, even if its effects on gameplay are reduced.

• Social aspect

Progressively more challenging raids are important events in the original game, forcing players not to neglect their military, and creating memorable stories and valuable resource sinks in the process. Meanwhile, trading serves as a resource tap and encourages players to maintain good relations with other colonies. Given the huge role that social features would play in engagement, enabling trading and combat with other players – even if players can choose whether to opt-in – would be important to include.

A player's pawns and turrets (right) attempt to hold off an attack from hostile robots (left)

Challenges

There are a few particular aspects of the original Rimworld that would need to be reworked or removed for our mobile game:

• Random events

Random events, as they exist currently, are simply not compatible with a persistent mobile adaptation of Rimworld, especially one that allows for PvP. After all, two players encountering different sets of random events and consequences will be in wildly different positions as their colonies grow, all else equal. Additionally, a persistent game of Rimworld would be running in the background more often than not, so players unable to access their phone would be at a major disadvantage. Random events will need to function in a way that is fairer for all players.

• Severity of consequences

Unless a player chooses otherwise, in the original Rimworld, players can always reload a save if they make a mistake or regret a decision. This is important because random events, inattention, or poor decision-making can potentially end a colony in mere minutes. A persistent, PvP-enabled game of Rimworld would be subject to even more dangers. Although many other mobile games allow players to make poor decisions, it is rare that those decisions can wipe out dozens or hundreds of hours or progress.

• Technical limitations

Rimworld is an incredibly processor-heavy game, which presents technical challenges for mobile. The minimum recommended CPU for PC Rimworld is an Intel Core2 Duo E8400, with over 6 times the thermal dissipation and over 60% higher base processing speed as the Snapdragon 865, the most powerful mobile gaming processor today. Even with the Core2 Duo and many more powerful processors, late-game performance slows to a crawl as colonies grow and more pawns occupy the game world. Somehow, technical performance will need to be significantly improved.

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Rimworld Mobile

Core Loop

The gameplay loop of our hypothetical adaptation, what we will call Rimworld Mobile, is nearly identical to that of the original.

While Rimworld is considered a colony sim, it may be more appropriate to call it a “colonist sim”. The game’s core activities revolve not around maintaining the colony itself – that is, the resources and structures – but rather the people, and the only actual fail state is for all pawns to die. With that in mind, all player actions in Rimworld Mobile contribute to the survival of the colonists, or pawns. In effect, building and growing the colony is simply a means to keep a greater number of pawns safe from increasingly deadly threats.

Rimworld Mobile – Core Gameplay Loop (Abridged)

To summarize, players will spend most of their time managing their pawns to ensure food availability, entertainment, shelter, and offensive and defensive capabilities are all attended to. All of these areas will be vital for keeping a growing number of colonists alive, and will require crafting, research, resource gathering, base design, and medical attention. As their base develops, they will be encouraged to relocate to progressively more challenging biomes with greater resources. Throughout this process, players will have the option to trade with other players and non-player factions in their server.

Where Rimworld Mobile primarily deviates from the original is in the simplification of the systems underlying the game world and player action, as well as the addition of PvP elements players can leverage for silver (the primary in-game currency) and other resources. Rimworld Mobile also deviates in its use of free-to-play monetization methods, which will be further discussed later. Otherwise, the above gameplay loop should look very familiar for any prior Rimworld players.

Solving Challenges

Randomness

In the interest of fairness, every map of a particular biome and terrain (river, caves, hills, and so forth) will have the same quantity and quality of resources, despite their randomly-generated layouts. Additionally, although players may be affected by minor percentage-based random events, more significant events will occur on a biome-wide level. On a long enough timeframe, all players are statistically likely to experience the same rate and magnitude of random events, and effectively have the same opportunities and setbacks as a result.

Consequences

Rimworld can be brutally difficult and emotionally devastating, given how quickly pawns can die or a colony can fall, right before the player’s eyes. In Rimworld Mobile, pawns can get sick, maimed, or killed in the same way, but these are not permanent. Players will have access to uncommon items called “regenerators” and “resurrector serums” – the latter of which actually exist in Rimworld but are far rarer and riskier – that restore pawns’ limbs and lives, respectively. Even if a player’s entire colony dies in a raid, a handful of pawns will be revived automatically, and a significant portion of resources will be retained, giving the player a chance to rebuild while still giving them sting of a crushing defeat.

In this video, an exploding turret during a raid (0:25) causes an unfortunate chain reaction

Technical Limitations

While a good number of Rimworld’s more interesting, active systems like gunplay and pawn behaviors rely on simulation, not all of them have to. The original game already obfuscates many ‘under-the-hood’ simulations that can easily be replaced with simple algorithms and probabilities that are orders of magnitude less taxing on a mobile CPU, and would not noticeably affect gameplay. These include:

- Resource placement

- Wildlife ecology

- Trade offers

- Raid timing

- Area climate

- Temperature

- Disease/infection progression

- Nonplayer faction behavior

- Lighting

- Wound effects

Making resources available automatically at crafting stations, rather than requiring pawns to run between stations and stockpiles, would also alleviate the CPU strain significantly, as would streamlining pawn work priorities.

Progression

In the early game, a player will be placed into a server, and begin by selecting a spot for their colony on the world map in one of the starter biomes, selecting for desired terrain and proximity to other factions. They will begin creating with base with 3 fairly basic, randomly-generated pawns and a handful of available buildings. Their max number of pawns, stockpile sizes, and available research will grow as they upgrade the ‘AI Core’ overseeing their base using rare materials. At this stage, they will begin researching to unlock new buildings and crafting options, as well as trade beacons allowing them to arrange trades before sending out their caravans. Raids will remain fairly straightforward, even as the strength of the attackers increases alongside the player’s Wealth, the total value of all colony resources and structures.

The move into the midgame will be marked by the player acquiring electricity. Many research options will become available at this point, as well as a wide range of upgrade options for equipment using natural resources or animal byproducts gained from hunting. Players actively using their pawns to explore and gather may have gained a few rare resources, but these will be few-and-far-between. Thus, they will be encouraged to resettle into more challenging but rewarding biomes, keeping essentially everything except for the structure of their original colony. Raids will become more sophisticated, with enemies having greater options to circumvent defenses. Meanwhile, players will learn about implants and other ways of upgrading pawns.

Finally, at the endgame, the player has maximized their AI Core. By this point, they likely have many highly-upgraded pawns and weapons, have nearly completed the research tree, and may have resettled 3 or 4 times. Raids plateau in difficulty and complexity, with high-level events offering greater challenges. As before, players’ primary goal will be keeping their pawns alive, but they will now be able to craft extremely powerful weapon upgrades and single-use defenses to help with that. Otherwise, players will largely be occupied with raids, trying new base designs and gameplay experiments, and exploring other biomes.

In the end, players will always have the option of getting additional save slots, allowing them to start new colonies on new servers, from the ground-up.

Rimworld world map, displaying a number of biomes and several dozen colonies

Social / PvP

Social gameplay broadly falls into two categories: friendly, and hostile.

Friendly social primarily consists of in-game cooperation through trading and mutual military support against raids. Players can invite their allies to view their bases, which may have in-game benefits. Out-of-game, players also have access to a social hub, where they can post pictures of their bases, as well as recordings of memorable raids or events. The social hub may be the single best way to tap into Rimworld Mobile’s potential for social storytelling.

Hostile social primarily consists of PvP raids on player colonies within a certain level range, as well as any caravans moving too close to another player’s colony. Attackers will attempt to reach the resource caches where resources and items are held. These raids, like PvE raids, serve as valuable resource sinks, forcing players not to neglect their base’s defenses. In a way, players get the opportunity to show off their bases here as well, albeit to a hostile player who may be more concerned with the base’s defenses than its aesthetic.

All of these features significantly enhance engagement and extend longevity, by giving players greater opportunities to interact, forming strong alliances or rivalries while building a community.

Live Ops

Rimworld Mobile offers many options for increasing engagement, retention, monetization (discussed below), and a multitude of other metrics.

1. Events - While there will always be minor random events limited to a player’s colony, and regional events affecting all players in a biome, there will also be scheduled ‘planetary events’. These cover all players in the game, across every server, and may provide valuable rewards or simply new challenges and achievements.

2. Kingdoms - An enhancement to the existing social gameplay, a guild or ‘kingdom’ feature could enable new methods of cooperation, as well as new quests. Kingdoms could also offer greater opportunities and rewards for raiding, and potentially even larger-scale guild conflicts incorporating the world map and territory.

3. Content - Simply adding new biomes, item upgrade paths, NPCs, and materials would further extend the game’s longevity and replayability. These can be brand new, or if a battle pass system is implemented (see Monetization below) consist of content previously time-locked

4. Challenges - Daily and weekly challenges – a mobile game staple – will keep players putting work into their colony, earning small quantities of currency and AI Core resources as a result. These may be incorporated into the in-game quests offered by other factions.

Monetization

Rimworld Mobile’s progression facilitates a fair monetization plan, in which all of the rewards provided through monetization are valuable, but can be earned in-game by free-to-play players without putting them at a gameplay disadvantage. Monetization will take the form of bundles with rare items, large quantities of basic resources, and code-locked items (which cannot be stolen during raids). Additionally, players can purchase crafting and skill boosts. Even if a ‘whale’ player gets far ahead in the game using these purchases, they will only be able to conduct PvP against players whose total item and resource wealth are similar. Even then, a well-thought-out colony and defenses can play a far greater role than equipment alone.

That being said, there are many potential alterations to Rimworld Mobile that could drastically change the gaming experience, as the game’s thriving mod scene indicates. Rather than monetizing resources and rare items, the game could offer a timed battle pass, granting players access to resource-boosted, one-off colonies with drastically different gameplay systems. These game modes could include new features like underwater colonies and magic, or new content like monsters and biomes. Either way, whether through novelty and new emergent gameplay, or through collaborations, these temporary game modes would need to be very promising.

Two popular Rimworld PC mods, A Rimworld of Magic (left) and Dinosauria (right)

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It seems unlikely that a mobile adaptation of Rimworld would ever be released. Ludeon Studios, the indie game studio behind Rimworld, has given no statement or indication to suggest so. However, there is interesting news on that front. Tynan Sylvester, founder of Ludeon Studios and mastermind behind the game, posted a tweet back in March putting out a call for new developers, and specifically referencing multiplayer. This could be an entirely new game, or just an official multiplayer update for Rimworld.

But maybe it isn’t?

If such an adaptation is conceived by Ludeon – or if any other ambitious developers try their hand at making something similar – hopefully it overcomes the same challenges and limitations I believe this outline has tackled. More importantly, I hope it retains the charm, emergent storytelling, and thrilling challenge of the original, and perhaps elevates them to a new level.