Pyroclasm is too puny for Commander, where pretty much everything is tougher than 2
Deploy planeswalkers that generate tokens, draw cards, and destroy threats all while stacking emblems and loyalty counters
What makes Memnarch a powerful Mono-Blue Commander is that the abilities do not require Memarch to become tapped, meaning you can use these abilities as much as you wish
Then Will of the Sultai will let you either mill three and then return all lands - nasty good here, or toss +1/+1 counters on a dork equal to your land count and trample for a turn, and if you control your leader
Collectible Cards - Surprise them with a rare or limited edition card to add to their collection
Once all this has been accomplished, the game will give your opponent one last chance to stop you