Minecraft wiki entry for Development_versions, associated text: Axolotls will spawn underground, in water.
Holding a bucket of tropical fish will cause nearby axolotls to follow the player on both land and water.
Axolotls cannot be tamed but they can be bred by feeding them buckets of tropical fish.
Axolotls will attack fish, squid, drowned, and guardians.
Axolotls come in a variety of colors, all with an equal chance of spawning except for blue.
Blue axolotls have a small chance of spawning as a mutation when breeding 2 axolotls.
Axolotls can survive on dry land for a few minutes. After that they will start to dry out and take continuous damage until rehydrated.
When taking damage, there is a chance that the axolotl will play dead. While playing dead, the axolotl will regenerate health and mobs will be unable to target the axolotl.
When a player kills a mob that the axolotl was attacking, they are rewarded with the regeneration effect, and their mining fatigue is removed if they have it.
Axolotls can be picked up with buckets, like fish.