Murphy doesn't suck on the wii u version. Essentially, there are certain interactive objects in some (no idea how many until the game is out) levels that require someone controlling murphy to interact with them.
Stuff like, slash ropes, flipping switches, etc. On the wii u, this is done by the gamepad screen controlling murphy, where (for example) you cut the ropes by moving the stylus/a finger over the rope. Optionally, you could have a second player be doing murphy for you while you're playing as rayman.
In the xbox/Ps3 versions, you have everything murphy does assigned to a single button and you have to pray you're close enough that he accepts your input properly.
Also, 5 player support is wii u only.