For this solution you need to eliminate 10 enemies with an explosion of TNT which can be carried on your head by pressing
and thrown using
I was having difficulty throwing the TNT as it always seemed to only catch 6-8 enemies.
An easy way around this I found was to get 10 enemies around you (Zombies are best as they get very close) with the TNT above your head and let them defeat you. As you die, your TNT will fall and eliminate all the enemies.
This can be accomplished here -