IGN is etherealboop
2nd submission
Name: Imitentacle
Cost: 2 
Health: 1100
Movement: 1 tile, walking by jumping slowly in the needed direction.
Attack range: all around itself in 1 tile by using its tentacles in all directions.
Damage: 400
Ability: A key investment
All of my ideas revolve around balancing resources and ability management, and this one isn’t an exception.
Spawn lock: 1 turn
Cooldown: 1 turn
Ability cost: 2 
Using the ability would let the character transform into its next form at the start of your next turn. You wouldn’t be able to transform him in that turn, but would be able to at the next.
The stats for the other forms would be:
Animation: Some long tentacles push the chest open, staying outside of the chest now to attack
Health: 1600
Movement: 2 tiles, crawling using the tentacles outside of the chest
Attack range: 2 tiles, using a single tentacle to smack the needed phobie
Damage: 450
Animation: More tentacles break through the bottom and the top of the chest, now giving the phobie full movement and range.
Health: 2100
Movement: 2 tiles.
Attack range: 2 tiles in a straight line, punches through an enemy right in first tile to the second tile, attacking both for 100% of the damage.
Damage: 550
Also a new ability replaces the old one when it reaches the final form!
Ability: Hittin’ the key spots
Cooldown: 2 turns
Attack range: 2 tile radius, 50% damage falloff on the 2nd tile
Attack: 700
This phobie would be an interesting pick either for the slow game against a (or as a) trapper, or for anyone who wants to play it slow and wait out a push from the opponent.
You’d basically get a 7-key phobie for the cost of 6 keys and some waiting! What could go wrong? Basically everything.