Lol thanks I'm thousandcuts btw. I calc'd it several times but I neglected to take Life Orb off the calc that day for some reason. My item was Psychic Gem of course.If the Cobalion was Jolly (which it may have been by accident) and had a Lum Berry/Leftovers (I think it's probably Lum or something; I don't see lefties recovery) then it wouldn't be that strong.
0- SpA Cobalion Hidden Power Ice vs. 0 HP / 4 SpD Flygon: 200-236 (66.44 - 78.4%) -- guaranteed 2HKO
However, if the Cobalion had Life Orb, and was Naive (aka no SPATK drop):
0 SpA Life Orb Cobalion Hidden Power Ice vs. 0 HP / 4 SpD Flygon: 291-343 (96.67 - 113.95%) -- guaranteed OHKO after Stealth Rock
btw, in the future try out PS!'s Damage Calc: http://pokemonshowdown.com/damagecalc/ if you need to see how much damage something does to something else. Verrrrry useful tool ;)
Hopefully I answered your question?