Critters and Companions Mod

Critters and Companions is an absolutely adorable mod that adds multiple mobs to the game, with a few of them having useful functionalities and some being decorative. You will find them in rivers, plains, the ocean and some other locations, with the Koi, Ferret, Otter, Dragonfly, Red Panda and Dumbo Octopus being some major examples.

Dragonflies can be tamed with spider eyes to help you out during combat, Otters will attack fish near them and eat whatever fish you right click them with, but they'll also open clams that you can get from fishing. This will get you pearls, that you can use to make a necklace that gives you major buffs for underwater exploration.

Ferrets can be tamed with raw rabbit and will dig for loot if you give them raw chicken, or assist you when looking for animals to hunt. 

If you find enough Koi Fish grouped together in a river, they'll give you a Luck buff.

This mod offers versions for both Forge and Fabric. Download links are given below.