Actual alien wildlife

[Gargrant]

Speaking of genetic splicing and the possibilities of even near-tech (to us), the MaddAddam Trilogy (Oryx and Crake, The Year of the Flood, MaddAddam) from Margaret Atwood has multiple wonderful examples of gene-splice animals and gene-tech:

Pigoons: pig-stock with human genes designed for organ harvesting.  In the wild, they are aggressive and intelligent pack hunters.
Rakunk: A cross of a skunk and raccoon - designed as a pet replacement, no scent and tamer than a raccoon
Snat: A rat/snake cross - a bio-weapon meant to be released on others
Bobkitten: A Bobcat/Domestic Cat cross meant to control the wild population of feral cats
Wolvogs: An animal that looks like a tame dog but has the mind of a wolf, designed as deceptive guard animals that can't be manipulated or made friends with
Chickienobs: A complicated chicken-esque creation designed to produce vast quantities of chicken-like breast meat, having a simple mouth chute and no brain beyond autonomic functions - essentially "chicken sea anemones", very disturbing to look at
Glowing Rabbits: A rabbit breed given the firefly luminscence genetics and designed to be amusing and interesting in park-lands.

Anyway, this is just a set of ideas from "near-future" fiction.  I highly recommend the books (especially Oryx and Crake), but they are not for kids.

[keylocke]

pikachu.

[Rahjital]

The timescale in Rimworld isn't really enough for any major evolution to happen, and it makes sense that humans bring Earth wildlife when colonising planets to remind them of home. It would be nice to have the real species evenly mixed with genetically modified animals (the boomrat and muffalo are already more interesting than the mundane Earth animals, and the muffalo isn't even special in anything).

Also, alien plants. It's nice having original animal species, but it will always be missing something if the game sticks to real plants only.