Place Bomb Tower in the middle of the lane against ground swarms and building-targeting cards (Hog Rider, Royal Hogs, Giant). The bomb it drops when destroyed damages troops around it. It's also effective against Graveyard.
Tips
Use it against multi-unit cards like Royal Hogs and Goblin Gang.
It can't hit air, so you need other cards against Balloon and Minions.
Try to have its death bomb go off next to enemy troops.
Strengths
Clears ground swarms and pulls building-targeting cards.