Name the best/worst fusions!

[vaiyt]

Which fictional characters would, if fused together into one being, be much greater than the sum of their parts?

This is less about raw power, and more about powersets that cover for each other's weaknesses, personality traits that allow the fusion to extract the most potential from themselves, loopholes in a setting's logic that can be exploited by the merged being's combination of talents, or a range of skills that can be stacked for multiplied effectiveness.

What about the converse? What characters would produce the worst result if merged? Which characters have the abilities that cancel each other, the most crippling stacks of flaws and the most incompatible combinations of personality and skills?

[KJS]

Good example: Johnny Sorrow and Manchester Black. An intangible character with insane energy manipulation powers can now use massively powerful telepathy and telekinesis while intangible too.

Bad examples: Rogue and Ghost. A character whose powers require touch is now covered in full body armour. Armour that has the primary power of turning the wearer intangible.

[StupidMoniker]

Flash and Zatanna, Deadman and Zatanna, Flash and Green Lantern, Basically any glass cannon is going to be improved immensely by being fused with someone that is either a speedster, intangible, or insanely durable. People that have immense power but are slow to act would be improved by speed.

[FennerMachine]

Superman and Doctor Strange. The Most powerful versions of both fused would be ridiculously powerful.

[Powerboy]

I'm not saying it would be one of the best but I'd love to see "Powerfist", the fusion of Luke Cage and Ironfist.

[BCaeser1]

I'm not saying it would be one of the best but I'd love to see "Powerfist", the fusion of Luke Cage and Ironfist.

How formidable would a being like "Powerfist" be? Thing or Colossus level? Higher?