The Hellfly is a Hard Mode Underworld enemy. Hellflies spawn in groups of three and swarm the player or stay at a distance to lob tiny fireballs at the player from their abdomen. When they spawn while Stan is present they gain a great boost to all stats, start slightly glowing and emitting fire particles. They also cause the 'On Fire!' debuff in this state. They can also be manually spawned by throwing Flies into lava. However, Hellflies spawned like this do not drop anything so this is mostly to annoy players when they accidentally throw a Fly into lava.
- 40 Damage + 20 when Stan is present. (Melee)
- 35 Damage + 15 when Stan is present. (Fireball)
- 20 Defense + 20 when Stan is present.
- 120 + 90 when Stan is present.
- Fly (100%)
- Fly Dust (10%)