When your castle is being under attack you have one massive hammer to solve the situation. Move with the hammer and hit everyone. Use special moves and tricks which can be bought in a shop.
The principle of the game is very simple. From both sides enemies approach, they can be destroyed from the close combat or throw some axes. It sounds simple but combining two moves in the right speed can be difficult. Use various elements for various enemies, yes, they vary. And gained money? Buy upgrades or more powerful spells.