Water Wren

Water Form. The elemental can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Non-threatening. The Water Wren is a tiny bird.  It is unable to grant advantage by flanking.  It may share its space with an allied creature.

Elemental. The water wren can breathe in air and water.

Freeze. If the elemental takes cold damage, it partially freezes; its speed is reduced by 20 feet until the end of its next turn.

Move Like Water. This creature's movement does not provoke opportunity attacks.

Echolocation. Once per round, as an action the Water Wren can let out a high pitched 'cheep'.  All creatures within 30ft on the same plane of existence become visible to the Water Wren until the end of the Water Wren's next turn.  If a creature located in this way moves, the Wren knows its last location.  Invisibility has no effect on this feature. If the Water Wren is under water, the range is extended to 120ft. If the Water Wren is within 10ft of a creature and uses this feature, that creature immediately knows the direction of the sound and has advantage on checks to percieve the Water Wren.  

Peck. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 1 piercing damage.