(Stealth Rock is omitted from these calcs as it's meant to showcase the synergy of Spikes and Mega Lopunny. Of course, these outcomes would be better with Stealth Rock up.)
252 Atk Lopunny-Mega High Jump Kick vs. 252 HP / 92 Def Ferrothorn: 324-384 (92 - 109%) -- 50% chance to OHKO after Leftovers recovery
252 Atk Lopunny-Mega High Jump Kick vs. 252 HP / 92 Def Ferrothorn: 324-384 (92 - 109%) -- guaranteed OHKO after 1 layer of Spikes and Leftovers recovery
252 Atk Lopunny-Mega High Jump Kick vs. 244 HP / 252+ Def Eviolite Chansey: 582-686 (82.9 - 97.7%) -- guaranteed 2HKO
252 Atk Lopunny-Mega High Jump Kick vs. 244 HP / 252+ Def Eviolite Chansey: 582-686 (82.9 - 97.7%) -- 68.8% chance to OHKO after 1 layer of Spikes
252 Atk Lopunny-Mega High Jump Kick vs. 244 HP / 252+ Def Eviolite Chansey: 582-686 (82.9 - 97.7%) -- 93.8% chance to OHKO after 2 layers of Spikes
252 Atk Lopunny-Mega Return vs. 248 HP / 8 Def Toxapex: 118-141 (38.9 - 46.5%) -- 90.2% chance to 2HKO after 3 layers of Spikes and Black Sludge recovery
252 Atk Lopunny-Mega High Jump Kick vs. 252 HP / 28 Def Tangrowth: 178-210 (44 - 51.9%) -- guaranteed 2HKO after 1 layer of Spikes
252 Atk Lopunny-Mega Return vs. 248 HP / 88 Def Venusaur-Mega: 135-159 (37.1 - 43.8%) -- 98.4% chance to 2HKO after 3 layers of Spikes
252 Atk Lopunny-Mega Return vs. 248 HP / 8 Def Gastrodon: 234-276 (55 - 64.9%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Lopunny-Mega High Jump Kick vs. 248 HP / 8 Def Gastrodon: 297-351 (69.8 - 82.5%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Lopunny-Mega High Jump Kick vs. 248 HP / 8 Def Gastrodon: 297-351 (69.8 - 82.5%) -- 56.3% chance to OHKO after 3 layers of Spikes and Leftovers recovery