I created a test quest using Fire Boomerang item as the start and the enemy is the bat. It takes a lot of hits (by boomerang, not trail). If I had edited the quest and set the Fire Boomerang's damage to 0, it takes 3 hits. The Fire Boomerang should kill the bat with one impact if damage is set to 0.
Is the Fire boomerang defaults messed up, or all boomerang defaults messed up, or not.
EDIT: Okay, the Fire Boomerang defaults are messed up. Damage is set to 2 and that is why it takes so many hits to kill a bat. Reset the damage to 0 and make it as default.
Another bug is that when damage set to 0 for the Fire Boomerang, it takes 3 hits (by boomerang, not trail) to kill a bat. That is one hit more than the Magic Boomerang. It should be 1 hit.
Before fixing this, can you check what the Fire Boomerang did back in 2.10?