After some thinking, I have conceptualized how these counterparts would look like and attack, sadly there is no name for these concept monsters.
Undead family rocket puppy counterpart (OLD, New concept in progress)
This guy wasn't too hard to think of: A howlitzer with an extra pair of smaller horns parallel to each other, larger and more sharper teeth with a pair of these teeth being even longer than the rest, and more menacing eyes. It attacks by opening it's mouth and makes it's head glow, the glowing of the head leaves the monster with an exhaling sound and becomes a projectile which is in the shape of it's head. Here's the thing though, unlike a rocket from a rocket puppy, it does not explode in a sense of a rocket but instead this head shaped projectile will chase you and bite you to death until it dissipates into status inflicting mist similar in function to a greaver's mist.
Slime family rocket puppy counterpart (OLD, click here to go to new less ridiculous concept.)
This also didn't take very long to conceptualize: A polyp whom spikes are more curved and longer to an extant of it being completely easy to identify from a normal polyp. This creature shoots a slime ball covered in spikes that also does not explode like a rocket from a rocket puppy, instead this slime ball of spikes will orbit the targeted knight and barrage the knight with spike projectiles until it explodes into 360 degrees of spikes flying all over the place.
Aren't howlitzers already rocket puppies in a way?
I'd rather just see Royal Polyps in more places than your suggestion.