Erayo, Soratami Ascendant
has a nuts ability if you can get her to flip. An opponent having to throw away one spell just to be able to play something every turn is absolutely backbreaking. The only problem is getting her to flip, since four spells in one turn is easier said than done. It's one thing to get enough mana together, but there are zero-mana spells out there. The real problem, to me, is having four cards in hand ready to go. Sure, one of those spells can be Erayo herself, and some number of them can be provided by your opponent if you play craftily, but can you always rely on that?
Enter her best friend Shrieking Drake - for you can play him, bounce him right back to your hand, and hey presto, that's a spell cast. Play the same Drake four times and you can flip Erayo with just one card. Don't want to leave her sitting around as removal bait beforehand? You can also play Erayo, Cloud of Faeries and a Drake twice to immediately flip her on turn four.
Once Erayo's flipped, Remand becomes an absolute killer, since your opponent has to throw a spell away to even get to the point of you delaying his follow-up. Counterspell works just as well before or after Erayo's Essence is online, keeping your opponent from blowing her Essence up or otherwise interfering with your plans. Of course, all the countering in the world can't save you from what's already in play. Even if you do flip Erayo, if your opponent had resolved a quick 4/4 beforehand, it can still beat you to death. Equilibrium can take care of whatever makes it into play, letting you bounce all the creatures you want for apiece when combined with Shrieking Drake.
So how do you win? Arixmethes, Slumbering Isle also is activated by playing multiple spells, though in his case they don't all have to be on one turn. Though a little pricey to play, he provides mana mid-game, then switches to a 12/12 bruiser after you drop the Drake enough times. Aetherflux Reservoir is a little more direct, as once you have control of the board, you can gain 15-20 life per turn just spamming the Drake and soon cash it in for an enormous blast that takes your opponent's head off.
