I was your opponent in this game and I can let you know my gardevoir's spread was 252 HP, 60 SpD so even a crit shouldn't KO (with spread damage as it was).
252 SpA Mega Charizard Y Heat Wave vs. 252 HP / 60 SpD Gardevoir in Sun on a critical hit: 133-157 (76 - 89.7%) -- guaranteed 2HKO...