This comic was originally created with Duke Nukem in mind I think the issue with the Duke is not attitude, but relevance.

He had some 2d games almost nobody knows, Duke Nukem 3d which made him popular decades ago and the remake which didn't do well. The chances of him getting in are as big as any unknown random protagonist from some old PC game at this point.

So I swapped to Mortal Kombat because while they are relevant, their gimmick is the gore and no way Nintendo would allow them to rip the spine of Mario.