Protect your gems against the King's good heroes by building various towers on tiles of the corresponding color. You're not allowed to build towers on forest tiles, but you can use a spell to cut down forests. Gather the evil forces, upgrade your towers and cast mighty spells, do whatever you can but don't let them touch your precious gems!
Use your mouse to play, hold Space bar to double the speed, press Enter key to call the next wave. You can also use hotkeys; 1 to build Den, 2 to build Crypt, 3 to build Temple, Q to cast Cut Out, W to cast Terror and E to cast Meteor spell.