Herpling

Nothing summons one. They start appearing on their own once the world has turned Hardmode, and what decides a spawn is the tile underfoot, not the biome readout in the corner. Crimson grass, crimstone, crimsand and red ice all count, anywhere in the world, and down in the underground layer crimtane ore does too. A vein of spread creeping toward your house quietly becomes a Herpling supply you never asked for.

Hopping is the whole moveset and it covers flat ground quicker than an early Hardmode character does. Knockback barely registers, so you cannot shove one off you once it has arrived, and the rhythm between leaps is irregular enough that you will misread the next one. Standing your ground and trading hits is a bad deal.

The jumps are long and low, which is the flaw. A platform a few tiles up, a ledge with one sheer face, or simply wings puts you somewhere it can only bounce around underneath. It runs the same behavior as the jungle Derpling and the two names are a matched pair. The Corruption never got a version of its own.