Worst:
-Logan and all the furball mutants are actually an entirely different species
-Azazel/Nightcrawler (he should've been Mystique & Destiny's child)
-Xorn is Magneto
-AvX Phoenix crap to justify Avengers being involved
-Original Flavor Mondo was just an evil spy
-Magneto's Roma erasure
-Scott has a brother
-Mystique & Sabretooth (honestly ew)
Best:
-Cipher
-Billy and Tommy being Wanda's reincarnated kids
-Pietro and Wanda being Erik's kids (and they still are)
-Magneto's Holocaust backstory
-Monet is/are the M-Twins but not really
-Penance is actually Monet but not really
-Graymalkin being under the school the entire time
-Pixie is Mastermind's daughter
-Scott has a brother