I'm thinking the Dynamicpunching Wooper might very well beat Metallus, yeah. This could be because a.) Dynamicpunch is super-effective against Steel, b.) Metallus might do himself serious harm in his confusion (be it confusion induced by a successful Dynamicpunch hit or simply induced by trying to get his head around the notion of a creature with no arms or even any hands being able to use that move), c.) the Wooper might opt to use the Beret of D00m, or d.) any combination of the above.