>>19362343252+ SpA Mega Abomasnow Blizzard vs. 252 HP / 252+ SpD Cresselia: 120-142 (27 - 31.9%) -- guaranteed 4HKO after hail damage and Leftovers recovery
252+ SpA Mega Abomasnow Blizzard vs. 252 HP / 252+ SpD Shuckle: 78-93 (31.9 - 38.1%) -- 93.1% chance to 3HKO after hail damage and Leftovers recovery
252 Atk Mega Abomasnow Wood Hammer vs. 252 HP / 252+ Def Shuckle: 76-91 (31.1 - 37.2%) -- 83.3% chance to 3HKO after hail damage and Leftovers recovery
252 Atk Mega Abomasnow Wood Hammer vs. 252 HP / 252+ Def Cresselia: 127-150 (28.6 - 33.7%) -- 0.6% chance to 3HKO after hail damage and Leftovers recovery
This is something that's bulkier than shuckle on either side, with screens, access to reliable recovery, access to calm mind and 85 base speed. Also Lunar Dance. Why are you talking about OU in this context anyway?