>>32067686here's a few calcs
+2 252+ Atk Huge Power Mawile-Mega Iron Head vs. 252 HP / 112 Def Sableye-Mega: 372-438 (122.3 - 144%) -- guaranteed OHKO
+2 252+ Atk Huge Power Mawile-Mega Sucker Punch vs. 0 HP / 0 Def Heatran: 274-323 (84.8 - 100%) -- 81.3% chance to OHKO after Stealth Rock
+2 252+ Atk Huge Power Mawile-Mega Iron Head vs. 0 HP / 0 Def Magearna: 438-516 (145.5 - 171.4%) -- guaranteed OHKO
+2 252+ Atk Huge Power Mawile-Mega Sucker Punch vs. 248 HP / 244+ Def Zapdos: 232-274 (60.5 - 71.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
+2 252+ Atk Huge Power Mawile-Mega Iron Head vs. 52 HP / 0 Def Buzzwole: 372-438 (101 - 119%) -- guaranteed OHKO
+1 252+ Atk Huge Power Mawile-Mega Iron Head vs. 0 HP / 4 Def Landorus-Therian: 402-474 (126 - 148.5%) -- guaranteed OHKO
i don't play OU myself but i know those are a few common mons in it