"In Troll Blaster, each level presents a new challenge for the player. The trolls are in structures to the right of the screen that are build of wood, stone, glass and metal. With an arsenal of four weapons, a cross bow, cannon, fire cannon and grenade launcher, the player must strategically select which weapon to use and in what order. Each weapon carries a different strength and has a different effect on the structures. The player must decide strategically which weapon is most appropriate to fire at different points within the structures to destroy the most trolls. Additionally, there is also an element of aim required as there are trolls that could only be killed by direct hits but require skill in aiming."
Source: The Developer Website.