Water Axolotl

Amphibious. The Axolotl can breathe equally well in water and air.

Blessing of the Torrent (Passive): When within 5 ft of their master, the master gains the same resistances and vulnerabilities it has as well as an additional 10 ft swimming speed. (Not immunities)

Hydrodynamic Movement. When in water, its movement speed is doubled and it can move through difficult terrain of water without penalty.

Camouflage (Aquatic). While in water, they can change their coloration to blend in with their surroundings, granting advantage on Dexterity (Stealth) checks.

Water Sense (Blindsight - Limited). Within 10-20 feet, they can perceive creatures and objects in water, even if they can't see them.

Spellcasting. The familiar can cast touch spells for their master, so long as they cast the spell and the Axolotl uses its reaction to make the spell attack. 

Dampen. Uses an action to manipulate the water particles in the air to extinguish a small flame (torch, candle) or create a water droplet on a surface.

Clean. Uses an action to purify a small amount of water (a cup or two).

Glow (Bioluminescence). Uses an action to cause itself or a small area of water to emit a faint, soft light (a natural glow, similar to deep-sea creatures) sheds dim light in a 5 ft radius centered on itself or a point in a body of water within 15 ft.