The yellow box worked well! I had more trouble with the dart and getting it to set the area that I wanted. I may need to try it again to give you a better description.
Ah, I think I understand! If you're throwing the dart, the aiming does gets a little wonky. I've had better success with impaling it onto the screen like a nail and releasing it. The dart is supposed to create fire in 3 blocks - at the point of contact and 2 tiles on either side.
I read that you played all 90 games over the weekend so I can't in good conscience ask you to strain your eyes any further this soon :p