So after doing a little testing my friend and I figured out that dealing damage to the enemy and THEN activating the fire cart makes the cart do damage. So the cart only does damage to enemies that have received damage from your Hero. This damage can come from basic attacks or abilities. Additional Notes: This was only tested on Squire and Huntress so not 100% confirmed on all classes. Also the fire cart can sometimes do DoT damage, but seems very random. Also dragons seem to take damage from fire cart as if it were working properly.