Metroid Larva "pet" that sucks the health out of enemies, then they evolve to an alpha metroid which charges at the enemies, dealing large amounts of damage and knocking enemies away, then evolving to an Gamma Metroid which does the same as an alpha metroid except it can fire a projectile (a nova laser-ish projectile) then to a Zeta Metroid, this time they aren't flying; but they are in the ground, they can ocassionally hop to reach flying enemies or to cause a shockwave to knock enemies up into the air and stun them, could spit "acid" from their mouth, and the simple swipe attack, massive knockback; next the Omega metroid, they are bigger, stronger, dealing MASSIVE amounts of damage, MASSIVE knockback, could make its mouth like a flamethrower, can also hop but not as high, and deals more damage than it did before; and lastly, the Queen Metroid, there can only be ONE in an entire world, they need a specificed place for her to stay and lay eggs, she is also very tanky, with large amounts of health (like 1k?) with its only attack to attack its victim with the head and "eat" it, after some enemies that were "eaten" she will lay an egg that CAN be destroyed, so take care of it, also take care of the Metroids, since they can be killed, and the more metroids you have, the weaker they are (less knockback, damage and health)
I know having Metroids as a "pet" or "friendly killing machine" sounds weird, but i thought it's a fun idea! I got the inspiration from the metroid larva pet that was in this mod around tconfig? or another metroid mod i'm unaware of, thanks for listening to my long idea.
EDIT: The zeta and omega metroid shockwave i mentioned is caused by the landing of the hop incase that isn't clear