Is there a way to unlock the Selendis portrait without playing 750 games in SC2?

Yes, you can unlock the Selendis portrait in Starcraft II by completing specific achievements rather than playing 750 games. One of the ways to do this is to reach a certain rank in the ranked ladder or complete particular in-game challenges that grant the portrait as a reward. Be sure to check the latest requirements in the game or on official forums, as they may change over time.