Bloodsports.TV (Steam key/Region free).

http://store.steampowered.com/app/336420/
Bloodsports.TV is a co-op top-down Hero Defense game. In this spin-off set in the world of Krater, take on waves of incoming enemies and bosses in this old school, fast-paced approach to strategic co-op games. Protect the glorious Missile Silo - locked on and ready to be fired at villages for a fresh supply of volunteers.

Team up with your friends and form a murderous crew from a variety of Gladiators, each with their own unique abilities and styles. Shoot, smash, stomp, electrocute, drain and melt your enemies (and occasionally heal your allies) to become a legendary Gladiator. Achieve higher scores and climb global leaderboards with your friends to become the greatest crew of Gladiators in the world.
Core Features:
8 Diverse Gladiators: Choose your favourite and team up with your friends to find the best strategies and survive the longest.
90+ Items: Customize your Gladiator to your liking with a plethora of items.
8 Arenas: A vicious sport of gladiators needs an arena. Bloodsports.TV features six arenas with tactics to master and beasts to slay.
Detailed Leaderboards: Track your performance against the global rankings or compare with your friends.
Path to Glory: Achieve your way through titles and unlocks to reach the ultimate honor - the title of Grand Master!
Co-operative Multiplayer: Play with your friends! Bloodsports.TV supports up to five players.
Drop-in, Drop-out: Reconnect a left session or join a group of friends as they are playing.
Scaling Difficulty: The difficulty of the game is based on the amount of players in the session, never worry about not having enough players.
Endless Mode: Up for a real challenge? See how far you can get in this mode of infinite carnage!
APOCALYMPICS: For the hardcore Gladiators out there, the peak of difficulty is contained within the legendary APOCALYMPICS. Only the best will survive this beast of a challenge.