Here's a list of some inconsistencies from the mother of all EU, Splinter of the Mind's Eye.

Darth Vader's lightsaber is described as blue instead of red.
Vader's and Halla claim that only a master of the Force can levitate objects, while that skill is commonplace in the prequel trilogy.
Vader's arm bleeds when Luke cuts it off, even though lightsabers cauterize wounds.
Vadr uses his hands to form a Force-globe of energy, but his hand are mechanical, which makes this impossible.