Boom Shroom: a small mushroom that has 2 legs. It will act like a creeper, explode. But instead of destroying blocks, it spreads spores which poisons the player.
Fire Ant: An insect that lurks in the Mesa biomes. Inspiration from This thread
Vulture: Well, you get the idea. A vulture.
Lava Spitter: A Snake-like creature that lurks the lava of the nether and spit Lava (particle) (Inspiration)
Hyena: like cougars, but has less health and speed. However, they attacks in groups.
Monkey and Baboon: Monkeys and Baboons are neutral. When attacked, all of the group will try to kill the player.
Really like the idea of Boom Shroom and Lava spitter ! But i don't if this "lorefriendly"!