Inspired by Lovecraftian horrors that inspire fear at their cosmic might and utter loss of sanity at their malevolent horribleness, Unstable Arithmetic is another way to overcome the inherent badness of Auras in Magic.
The age-old problem with Auras is losing two cards for one when your opponent uncorks Terminate or good old Terror. Wizards has largely solved the problem with Equipment, but they’ve kept trying to find ways to make Auras playable. The umbras did a straightforward job of it (Hyena Umbra is a nice example). There must be other, more subtle ways to get some benefit out of an Aura even if it (and the creature it’s attached to) dies.
Unstable Arithmetic is still a pretty risky card. It does nothing unless it sticks around until your upkeep, so there’s still a good chance you’ll get 2-for-1ed. Maybe giving it Flash would alleviate the problem. But if it does stick around, your creature is going to get absurd PDQ. It will double in size every single upkeep. Sure, a 1/1 won’t become a 4/4 until two turns after you cast it, but play it on a 3/3 and you’ll have a beast that dominates the battlefield in no time.
When the time comes for it to die (as all creatures do, eventually), you can yank all the counters off of it to crumble your opponent’s sanity, milling her deck a bunch. In a limited game with 40-card decks, this could get big enough to end the game, especially if you end up in one of those creature standoffs where no one can attack for eight turns in a row. It could work well in constructed mill decks too, sitting back as an ever-growing defender while setting up for the library kill. If a mill strategy isn’t your thing, you can blast away your own sanity (and library) to fill your graveyard with reanimate targets or dredge fuel.
There are a few nutty combos you can create with this too. Doubling Season and Paradox Haze come to mind. Theoretically, if you put Unstable Arithmetic onto a 2/2 with both of those enchantments out, it would be an 18/18 on your next turn. The turn after? 162/162.
I made this a hybrid card because it’s one of the cosmic cards in Fatewar, Robot Viking’s hypothetical Magic set. The two abilities are clearly green and blue, respectively, sort of a cross between Scute Mob or Chameleon Colossus and any blue mill creature you care to mention. It could easily be a gold card instead of hybrid.