Each character has to fight one type of enemy:

The knight fights only the orcs - if the knight's level is equal or superior to the orc's level.
The rogue fights only the zombies - if the rogue's level is equal or superior to the zombie's level.
The necromancer fights only the graves - if the necromancer's level is equal or superior to the graves's level.
The wizard fights only the ghost - if the wizard's level is equal or superior to the ghost's level.

Keyboard keys:
. ARROWS = move
. X = action
. C = switch heroes
. ENTER = restart game/level