Lineage System

The Lineage System determines which creature type re-spawns in a den when killed by the player. This only affects certain dens in game; normal dens only ever spawn a single type of creature.

Explanation
When a creature is killed by the player, there is a 33% (50% for, , and ) chance per cycle of that creature respawning in the parent den. For lineage dens, when that respawn chance is fulfilled, there is an additional chance that a different (usually stronger) type of creature spawns instead, based on a predefined lineage list. This is the only way to encounter s, s and s in game as and.

Information on Lineage lists for specific dens can be found in Rainworld > RainWorld_Data > StreamingAssets > world > [specific region] > world.txt, as well as in this interactive map Made by Henpemaz

With Downpour enabled, vanilla region lineages are found in StreamingAssets > mods > moreslugcats > modify > world > [region] > world.txt. For regions added in the DLC, moreslugcats > world > [region] > world.txt. Note that while vanilla regions are found in this folder, they don't contain world.txt. Refer to [this] map with Downpour on.

Examples
In this image, SU_A40 shows the room code, and : 2 : is the den number. The first type of Lizard to spawn in this den is always. When killed by the player, there is a 10% chance (0.1 out of 1.0 total) that the next Lizard spawning is instead. Every time the Pink Lizard is killed, there is then a 50% chance of changing to, and so on. The here re-spawns infinitely, since there is a 0% chance of progression. In this image, the NONE value means that nothing spawns in that den from game start, with a 5% chance per cycle of a appearing. After it is replaced with another Mimic (40% chance per kill), there is then another 40% chance that a instead appears.

Curly brackets { } indicate the size of the creature, if applicable, and can also be seen with.

Death Glitch
In game versions between 1.5 and 1.8, injured creatures do not regain health at the end of a cycle and so remain in their den indefinitely. It is possible to despawn entire regions this way. This can be fixed by installing Deathfix, which is also included in the ManyMoreFixes mod.

This glitch was patched out in the Downpour Update, but can be enabled with the Remix option Vanilla Exploits.