Oh boy do I love spending an unnecessary amount of time on detailing self-indulgent fictional settings. Sorry, no doodles, I hope the written description make up for it.
Planet name: Zerbrechen
Planet type: Floating chunks of solid matter bound together by gravity, was hit by an asteroid a few millenia ago and is still in the process of reforming itself into a proper planet. The core has already formed, and now the outer shell is slowly coming together. Earthquakes, volcanoes and all sorts of natural disasters are alarmingly frequent.
Can humans live there? Nope. Atmosphere composed mainly of argon fluorohydride, the main species inhales the compound, breaking the weak links between fluorine, hydrogen and argon with a low-energy metabolical process and exhales the argon, basing most of its breathing on hydrogen fluoride.
Main species: Now extinct, the Zerbrechans (fragmentum ambulans) were double-jointed mammalians with a few rather distinct features: the ehnerslitzen, situated in the average Zerbrechan citizen's neck, served as an exit for periodic puffs of argon gas, built up in the creatures lungs as it breathed the atmospheric gas in. Zerbrechans had two fingers and an opposable digit, which was definitively not suited for drawing in human standarts. That didn't stop them from trying, and the cultural output of bad scribbles was huge, especially during what many Zerbrechan sociologists posteriorly named The Rednascence, a period where Zerbrechan artists mastered a second color besides disappointing mauve: faint red. Sexual intercourse between members of the species was extremely complex, making full use of their double joints, underwater breathing capability and in some cases, the ehnerslitzen. The sexual act complexity's probably contributed a great deal to their extinction, the few Zerbrechans that survived the impact would rather watch their species fall into oblivion than go there. There are a few Zerbrechan ruins to be found, in fact, and be fully explored. High caution is advised, since the full psychological implications of being exposed to the Zerbrechans tenebrous frescos are unexplored.