Mo' Creatures is a mod the adds a lot mo' creatures. It adds all types off friendly and hostile mobs that will populate your world. It adds everything from horses which you can saddle, ride everywhere, and even breed, to the dreaded ogre which flattens landscapes. If you want to disable some or all of these creatures you can edit the settings found in Menu/Options/Global Mod Settings/DrZhark's Mo'Creatures.
There is no complete independent wiki for Mo' creatures but the actual minercaft wiki has a great page here; http://www.minecraftwiki.net/wiki/Mods/Mo%27_Creatures