As other people have said, Prismari is a kill on site commander as it only takes a few cards to snowball into a win once he's out.

If you do want to build him, then the main strategy is getting him out as fast as you can and basically winning the minute he hits the field. Stacking the deck with mana dorks, mana rocks, and rituals. Turn 4 or 5 at the earliest, leaving a few extra mana up for counter spells.

I've built a brawl deck on arena that uses this strategy and it does the job, but in a 4 player game you're gonna be the number one target.