Onslaught 2 - beta version of famous tower defense game. What makes this one any different from the rest? As with other tower defense games, you earn cash by obliterating the attackers that creep their way around any one of several maps available to play. With the cash you can purchase additional turrets or upgrade existing ones. But it is the Combos that add a level of depth to this tower defense game not present in other games like it. The combinations are many, and the resulting strategy becomes deep.