Icy Merman

Hardmode, the ice biome, no summon. It walks until it has line of sight on you, then plants itself and starts spitting, which is the most exploitable habit any enemy in the biome has.

A stationary target that fires slowly is free damage for anything that fires quickly. A Phoenix Blaster will hold it in place and kill it without it ever closing the distance, and a Nimbus Rod parked over its head does the work while you handle whatever else is in the cave. Melee is fine too, as long as you get in before it sees you.

Every spit chills you and now and then one freezes you outright. Neither is much alone, but the ice biome rarely gives you one enemy at a time. Once chilled you cannot reliably cross open ground to reach it, so you take another spit on the way in, and the freeze that follows leaves you standing still while the rest of the room arrives. If the first hit lands and you are still out in the open, back off behind cover rather than pushing through.

The spit is the enemy version of what a Frost Staff does, thrown out less often than the staff manages. Against the Ice Elemental, the other thing in the biome that shoots at you, these come faster and hurt less. Learn to read one and you have read the other.

• It cannot swim. A merman with no water mobility at all is a strange thing to commit to, but there it is.
• Its original sprite was a recolor of the merfolk form the player gets from Neptune's Shell.