Source: https://github.com/FatherToast/SpecialAI
Discussion: https://discord.gg/GFTzTdX

In short, this mod introduces variants to your default Minecraft mobs, such as creepers with fiery explosions, skeletons that shoot poisoned arrows, and zombies that leap at you. Not only that, but it allows you to adjust all support mob attributes and capabilities!
Each mob added by this mod has an adjustable rate that affects how common it is, from never appearing to being the only mob that ever appears!
This mod is highly configurable and each feature has at least one config option associated with it.
Browsing the configs will provide information on all the mod's features. If more in-depth information is needed, ask in the Discord server.