This is a game I found to be rather challenging but at an enjoyable level. I did find some bugs when selecting units though.
2D Tower Defense
How to play
There're 4 types of card you can use to defense the portal from the zombies, try not to let them destroy the End Portal.
+ Soldier 0.5 dmg per hit, shoot 3 bullets
+ Minigunner 1 dmg per hit rapid fire no reload, shoot 100 bullets
+ Accelerator 10 dmg per hit rapid-fire costs a lot of money
+ Ranger 40dmg per hit 6 sec reload
+ Farm 100 cash each wave
Pls comment when you won my game :D