While the first two Un -sets were designed to be drafted and played alongside other black-bordered cards, Unstable was best drafted alone
As proliferate is an incredibly flexible mechanic capable of interacting with any type of counter, Atraxa can be used to add additional loyalty counters to planeswalkers or improve creatures through additional +1/+1 counters.
If you can cast this with no lands and a bunch of mana rocks, you get a nice lock going, but its far away from mass land destruction cards
Wait, what was that middle thing you said
So if you play a creature, and your opponent casts a spell that kills it, but you counter that spell, but your opponent counters that counter, the Stack helps you figure out what exactly happened amidst the chaos of all that spell-slinging