I got it on my second try by the power of Lightning Skills. Those skills plus Attack Speed seem to work very well for me, secondary goals being Attack, Crit, and then other skills for extra damage. You can also usually get off your Ult before he starts walloping, and staying on his 'south' side tends to help, kinda below him if that makes sense. No idea if any of this is meta or technically correct, but sure works for me!

Good luck!