You can presumably cast anything you find off it since you already had the mana to cast the Mage, which could include mana rocks like Chromatic Lantern and Worn Powerstone, or disruptive pieces like Trinisphere and Static Orb
In a fully stocked bench setup, Sneasel could routinely swing for up to 120 damage on the second turn of the game
In conjunction with Naban, Dean of Iteration, it can be incredibly powerful by stealing the opponent's two best creatures, although something like a Lightning Bolt, Path to Exile, or Fatal Push undoes all of our work by giving the creatures back
The first problem of course is that Magic relies on twenty years worth of cards
I dont see them getting substantially worse anytime soon, as they count as permanents and can help you cast cards before you should be able to in a game of Magic, as Garfield intended