The Defenders: The Second Wave (Steam key/Region free).

http://store.steampowered.com/app/351400/The_Defenders_The_Second_Wave/
Fight the ghosts through 50 waves of growing danger. Play as a powerful wizard, a mighty warrior, or a strategic builder to stop the ghost invasion. Evolve your character in the direction you want. Survive until dawn, or die trying.

Features:
Awesome one to four player hack´n´slashing
50 waves of evil dudes to fight
10+ enemy types, each providing a new challenge
5 big, mean, evil bosses
12 different spells to fight off the enemies
6 tactical things to place to help you in the battle
25 items to buy to improve your defender
You can even bring down the moon
... also sheep!