i must credit @smoky salmon since this is literally based off his idea, however it wasn't fleshed out as much so i've done it myself
I had an idea of Gloomothra's spawn mechanic.
So how is it spawn is that, you craft a strange item which is made of 4 pure darkness, 4 tectonic shard and 1 occult gem and give it to Gloomoth which indicates with it's strange particle and then kill them however instead of dying it will turn into an egg which is a whole block long. Obviously it takes time before it hatches naturally and once it hatches/rebirths as a larva.
Gloomothra Larva, is a neutral mob who can be transport and has an ability to spew out sticky silk that temporarily freezes mobs, however it still cannot properly combat.
To grow them, you must offer them into underzealot, it goes like usual way of offering however it takes longer for it to before it succeeds, after some time a big pupa will appear with every underzealot covered in silk which connects to the pupa, which indicates that it will suck it's life back to them.
This entire process takes 5 minecraft days to fully done, once it is done, it will hatch as "The Gloomothra"!
Gloomothra is not a great fighter unlike Tremorzilla but can aid you on the battle, they can heal you and your pets.
Obviously it can combat to an extent like use its arms to knock enemies out, it can even fight midair by using it's wings to flap a sonar wave similar to Forsaken which can knock mobs away whilst taking damage in larger range, which gives her an advantage but is not capable of taking down someone as strong as Luxtructosaurus due to its HP.
(Feel free to suggest for it's ability)
One of its most recognizable ability is Rebirth, when it is killed there's a chance an egg is dropped which will then again cycle the entire process.
Another thing is that Gloomothra and Tremorzilla get well along, they're a great combination for combatting stronger mobs like Luxtructosaurus

@sudden herald, you have reached the level 2!