Monster Name: Phage, aka the Vanishing Colossus
Dont have an original concept image of my own
The monster is huge and towers over the players unlike other monsters who are roughly 2-3x the height of the players.
(I originally had this idea way back when the game was first announced, not that Attack on Titan is a thing I imagine the battle would be akin to that). When evolving rather than increasing in size the monster would actually just appear more formidable and look as though he is gaining armor (but not really, hes just getting a bulkier appearance).
(Because of its size it doesnt have normal attacks, instead they are in the Loadouts)
Stomp: A ground AOE attack where the towering monster slams his leg into the ground. With upgraded forms offering a dust kick up to temporarily blind and incapacitate hunters or lower their accuracy (though the Phage is still huge so hard to miss him)
Grasp: The Phage attempts to grab a nearby hunter and DOT them similar to the carnivorous plants. The hunters could of course free themselves from this, or could take advantage as this would give them better position to hit some critical points on the Phage like its face while they themselves are still taking damage. Or their partners could try and free them by shooting the hand.
Bellow: Lets out a mighty roar that has a small range and causes knockback
Club Arm: Throws a mighty punch at a direction in front of him.
Warp: Has a long cooldown that increases every time it evolves. Only has 1 charge to use. Lets the Phage sort of teleport from one place to another. Whether used for escaping combat or entering it, this would add a great level of suspense and tension as the hunters would never know if they are about to become the hunted with the Phage spawning right in the middle of their group. When you use the monsters actual body becomes still and vulnerable while the player is able to freely move around in free camera in a radius around the monster to spawn at a different location. It would be similar to a monster moving regularly with a 360 degree angle of vision (possibly make this marked by a glowing green wisp as an indicator to show where the hunters where the monster would spawn if this is too OP lol less funny though). Outside of this ability, the Phage would be rather slow moving. Not cripplingly slow, but they would probably be one of the slower monsters in terms of speed because of their grand and bulky height
Picks them up off the ground and puts the whole thing into his mouth. Doesnt even need to fight em. But depending on what he has eaten may take longer to consume meaning it will take longer to gain that buff/armor and the hunters may be upon him by then.