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May i point out that Heatran becomes a VERY solid wall if GO comes to OU, it checks one of GO's STABs, it checks Fairies, which become good due to being GO checks, and it checks what I consider the main threat to GO if it comes to OU, Bisharp. The only weakness it had to overcome is Ground type...
Darkrai A+ -> S-
and
Lugia A-> A+
Darkrai reasoning:
A Dark Void/Nasty Plot sweeper set with a sash can set up on practically anyone, and the only pokemon who really wall it are Klefki and Ho-Oh. Xern is a check, but not a true counter to this set.
Darkrai @ Focus Sash
Ability: Bad Dreams...
Dark + Fairy type Purrloin
The Aesthetics are all there, It looks so cute, and like it is plotting to rip your head out. It reminds me of those fairies that pretend to be something else, and lure you to their base to eat you.
It would give it some solid resistances (Particularly Fighting) as...