First of all, Mega Absol is banned from RU so it won't be added until a retest happens. Even so the performance of a mon in an upper tier won't make them added again.
And for the Barbaracle thing:
+2 252 Atk Barbaracle Stone Edge vs. 0 HP / 0 Def Shaymin: 280-331 (82.1 - 97%) -- guaranteed 2HKO...