Fritz

Fritz exists only while a solar eclipse runs in a hardmode world. Nothing summons him individually. He is part of that wave and arrives on foot with the rest of the ground crowd.

He sprints faster than almost anything else in the event and finishes with a jump. That combination beats retreating on foot. If your plan involves a slow swing or a weapon that needs charging, he is the one who ruins it, because the gap you left closes in a second and the jump carries him over whatever you put in the way.

Height beats distance. Fight from a platform a few blocks up and the jump falls short, which leaves him pacing underneath you as a free target. On flat ground, use something that lands damage the moment you press the button. He does not have the health to survive being hit properly. He only has to be hit.

Both the name and the hunched back point at the 1931 Frankenstein film, where the doctor's assistant is Fritz rather than Igor. A green skinned version of him sits unused in the game files.