Genome Guardian - Lunch time with Maw! 

The Maw turret proves again why Genome Guardian is one of the most creative roguelites out there. It constantly loses health but you can eat enemies that collide with your "mouth" to get health back.
This turret is best paired with the magnet, which reverses the effect of knockback. I also use blubber, which doubles my hitbox, making it easier to eat enemies.