Click (or tap) and drag tiles of the same type to cast a spell. Spells can either damage an enemy (whilst you're fighting them), or grant you more time in the dungeon (when you're not). The longer the spell chain, the more damage you'll do (or time you'll receive).
There are four types of spell (Earth, Water, Air, and Fire), each belonging to an elemental school of magic. Enemies also belong to a school of magic, and will be strong to and weak against certain elements.
Imp: Fire elemental, strong against Fire, weak to Water
Frost Giant: Water elemental, strong against Water, weak to Fire
Lasher: Earth elemental, strong against Earth, weak to Air
Banshee: Air elemental, strong against Air, weak to the 13kb size limit :]
How long can you survive in the Tiny Dungeon? GL HF!