Deathtrap

Be clever, be quick – and show no mercy.
Deathtrap is a unique Tower Defense game with strong action-RPG elements - a game of vicious tricks, killing machines, rotating blades and splattering blood.
Beyond the veil of this world, there is a chain of strongholds that were once built to keep the horrors of the void at bay. And now the monsters are returning from the depths to conquer and kill: only you can stop the monsters before they break through to the everyday world.
Enter a truly grim fantasy netherworld, choose your hero and defend the silent forts: use, rebuild and improve those ancient traps and magical machines in incredible single player and cooperative campaigns!
As one of the 3 distinct specialist classes - Mercenary, Sorceress, and Marksman - fend off more than 40 types of invaders with 25 deadly traps and more than 150 trap upgrades, not to mention the very special upgrades, which are tied to challenging and fun achievements. Solve rewarding side quests, find the hidden corners on the maps and hunt down the neutral creatures hiding away from the battle for even more exclusive loot.
Your Official Deathtrap Steam Key gives you:

Brand new ways to deal with those annoying invaders. 
Other heroes to team up with and save the world together in a cooperative campaign with specially designed maps... 
…or you can just show your friends your true personality: Players can set against each other in this game mode, where the defender prepares traps and defensive tactics, while the attacker has the ability to possess and control directly any creature in his or her army and employs skills to weaken the opponent or boost the invaders. 
An integrated Map Editor and Monster Editor which allows the creation of the user generated content; moreover, you can also share your deadly, cunning levels and challenging mini-campaigns with others. 
The goriest Tower Defense game ever.