Simply win 35 games, cumulative across both single-player and multiplayer.
Ways to Complete
The best advice for this achievement is just to find a character you enjoy playing with, who fits your playstyle, get a good deck build going, and have at it. If you're also considering going for the "100% Orange Juice" achievement, you might go about beating campaign mode first, since 4 campaigns with 6 levels each comes to 24 wins, plus the 5 extra scenarios puts you at 29 wins total. Grind out 6 more multiplayer wins from there, and you have your 35 games.