This idea may sound familiar (like the bio waste collection mission), but what I'm thinking is a planet covered in bio waste. Contact with the crust will inflict damage and corrosion which will cause slow damage on any part that is corroded. There will be no events on this planet (aka nests, or snake eggs) instead, you must kill a certain number of mutants, which will jump up to your ship to attack it. Furthermore, the mutant will also inflict corrosion, making it harder to kill them. Mutants are weak to cryogenic attacks and though they cannot be frozen, they will take double the damage that a kinetic attack would deal.
Leave any ideas or suggestions!
PS: maybe corrosion could be a weapon effect?