Ape - The Jungle (tropical) set has an ape one-shot, both close and distant, as well a monkey hoots element, as does the Tiger Battle set. Sci-Fi player’s Kaiju Island also has a giant ape element. Misgivings House also has a “monkey head” one-shot with some very loud monkey sounds. Ettin Battle has chest beating and great big feet elements.
Snake - For snake-y combat, I recommend Angel in the Tower, the mood “Xanesha”. Turn off the ambient noises (creaking stairs and whatnot) and go with just her sounds. The Xanesha is a lamia, a half-snake, and her serpent noises are excellent. Fort Rannick’s Lucrecia mood is also a lamia fight with more snake goodness!
Skeletons - Undead Battle and Zombie Battle both have some bony sounds, and Nightgaunt Battle has a great skeleton bones element, and Shadow Giants as a good skeleton crackles element.
I hope that helps!