Since Dark Souls is one of the few RPGs where you can use a shield as your primary weapon, it is clear that it needs a proper Captain America shield mod. Here's one, made by the talented modder l2dusk.
The mod works with the PC version of the game, and replaces the Iron Round Shield's textures to make it look like the vibranium one from the Marvel Universe:
Here's a short clip with some action. The Red Skull skeletons? Those are just a bonus. Captain America needs proper enemies, even in Dark Souls:
Dark Souls - Captain America Shield Mod [YouTube]