Unsurmountable? You must mean insurmountable. Nevertheless, be more specific.
Examples:
-Metaknight's Infinite Dimensional Cape is broken. When done correctly, it makes the game virtually unplayable, and ensures that the MK automatically wins when he gets the lead.
-Metaknight's Planking is broken. When done correctly, there is a 6-frame window where MK can be hit, and in these 6 frames, he is covered by a large, disjointed hitbox above him. He can make himself immune to dropped items or lava or long-lasting projectiles with the IDC method. If you manage to play perfectly, the most you can do is grab the ledge from him, which also proves no solution because now you are in lag on the ledge, and MK has time to get on the stage and either edgeguard you like an *** or just run to the other ledge.
-Metaknight's Tornado is not broken. It makes some matchups incredibly hard, it has absurd risk/reward, but it is definitely realistically (and relatively easily for most, I might add) beatable.
-Game and Watch's planking is not broken. It is a position where he has a lot of advantages, and can be hard to beat (really hard) with the right mixups, but you can definitely beat it within reason.
I don't know what you mean with being more specific. Do you have a different definition of broken? Why would you ban G&W's planking if it's beatable?