The firebreather has to shoot these 3 rows.
Remove the marked blocks to prepare him
for the right positions.

Get the stonehead monster to position 'A'.
This way he can destroy one cyan block on the left.

Drop down the firebreather to the 2 rows.
One block will be destroyed by the stonehead.
One block can be removed using the green hammer.

The mystery can be found under this skull block.