I bet this mod can be more balanced.
It could be more balanced by having the super large/powerful bosses (except crabzilla) shouldn't spawn naturally, but instead have their spawn eggs rarely be dropped from mobs that are similar to them. For instance, ursa major's spawn egg would be obtained from the bear mob. Also, the garble, manticore, and the pheonix should only spawn in the nether, but their spawn rate shouldn't be crazy. Leviathan and the cragadile should only spawn in the ocean biome.
Hurricane, if you're reading this, I'd appreciate it if you could implement these features into your mod