I have n idea for a boss. It is called The Lurker Below. It is an aquatic miniboss, an appearance similar to the lurker but with larger body, scales and a dragon head, has 200 hearts of health, 50% damage reduction and some special abilities. These abilities include:
Bite : It used this special ability when you are close, dealing 10 hearts of damage to unarmored players.
Poison Spit : It spits out a poisonous goo ball. The goo ball poisons and slows you.
Poison Blood: If it's attacked with a sword, it's wound will poison II you for 5 seconds.
Headram: It will spin around and ram it's head like a drill against the crag rock, destroying several blocks. This attack is crucial to avoid the next attack, but if you get hit by this attack, you will lose 20 hearts of health when unarmored.
Acid Rain: It will spit poisonous and acidic water combined with it's own saliva. this attack covers 16x16 area, deals magic damage and could kill you in 4 seconds if you did not shelter from this attack. It lasts for 6 seconds
Bubble: It will breathe out 5 poisonous bubble from it's snout. The bubble wouldn't harm you if you don't attack it.
You must shoot arrows to it's mouth while it's mouth is wide open to deal extra damage to the boss.