Vilgax

Vilgax is Ben's toughest enemy by far. He seems to be immune to a lot of attacks. Some of them are, Heatblast's fireballs, Diamondhead's diamond shards, Fourarms' strength, cannonbolt's cannonball ram, and a lot more. He is a gigantic alien, being the same size as Fourarms, or possibly even bigger. He has immense strength and endurance, and he also has some machinery in his arms which allow his arms to grow to an even bigger size, giving him even more strength.