Step 1: TNT
Make a 6x6x6 tnt cube
Step 2: Face
When chosen a front, put the creeper face with black wool.
Step 3: Front of Face
Using light green wool cover the tnt on the front
Step 4: Cover All
Cover all the tnt in light green wool except one block on the top
Step 5: BOOM
When ready light the tnt on the one block you didn't cover.