Alex's Mobs Add-on 1.21+/1.20+

Mod Alex's Mobs will add new mobs and animals to Minecraft, which will bring variety to the survival mode. From tiny Frogs to mythical Phoenixes — unusual and deeply crafted creatures will offer a unique gameplay experience.

We won't tell about all the creatures and their behavior — it's better to watch the video below to learn all the details of the add-on from the author himself.