If you use the ice staff on the fiery remains of a lavae who died, then the server will crash. This crash doesn't seem to happen with flingomatic, waterballoons, luxury fan, or extinguishing with ice - just with the ice staff. Maybe something to do with its projectile.
unfortunately not an uncommon bug because people try to save their items from fire with ice staves during this fight. that's how my friend and I stumbled upon it.
go to dragonfly, reduce its HP to 80% by any means just so that he starts summoning lavae, I waited 30 seconds so that the first lavae dies due to the death timer, then used an ice staff on the fires that it left on death. server will crash.