Onslaught 2 - great tower defense online flash game. The enemies are coming. They are trying to fight their way into Area 51 and it's up to you to build the defenses and stop them getting in! There is a cash bounty on the head of each attacker, and each wave is tougher than the last. Spend your winnings on upgrades to your defenses to keep the attackers at bay. The hit points of the attackers increase with 120%, so be sure to upgrade your towers.