This strategy can be stopped by fake out, taunt, encore, follow me, trick room, snarl, rage powder, and parting shot. Additionally, these Pokemon can OHKO one of yours with their most common moveset.
252 SpA Whimsicott Moonblast vs. 0 HP / 0 SpD Hydreigon: 480-568 (147.6 - 174.7%) -- guaranteed OHKO
252 Atk Genesect U-turn vs. 252 HP / 128 Def Malamar: 420-496 (111.7 - 131.9%) -- guaranteed OHKO
252+ Atk Choice Band Zygarde Superpower vs. 0 HP / 0 Def Hydreigon: 392-462 (120.6 - 142.1%) -- guaranteed OHKO
0 SpA Diancie Moonblast vs. 0 HP / 0 SpD Hydreigon: 448-532 (137.8 - 163.6%) -- guaranteed OHKO
144 SpA Tapu Fini Moonblast vs. 0 HP / 0 SpD Hydreigon: 496-588 (152.6 - 180.9%) -- guaranteed OHKO
252+ Atk Choice Band Dracovish Fishious Rend (170 BP) vs. 252 HP / 128 Def Malamar: 343-405 (91.2 - 107.7%) -- 50% chance to OHKO
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So the average team probably carries at least 2 or 3 checks to your strategy, even though they don't specifically prepare for it. It's not worth using.
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