Fourarms has no special abilities and his strength isn’t that special. You could count his extra arms as a special ability, but he barely uses them! Which makes sense, because extra arms aren’t that useful. And he’s pretty strong, but Ripjaws and even Stinkfly can tear through steel, and Diamondhead and Wildmutt are also great at melee combat, so Ben’s rarely lacking in strength. At least Humungusaur and Waybig are big! Fourarms has nothing going for him! In My opinion, he’s less useful than Grey Matter.

I think half the time Ben gets the wrong alien is just the Omnitrix going “No, Fourarms is shit, here’s a better alien”