Epic art
In principle I really like this card, but the problem is that it is too strong. There are a LOT of spells that this would affect, and you haven't even listed them all in the card desc. Shard of sacrifice and all of the area spells (pandemonium, firestorm, desiccation, plague) are ones that immediately come to mind. Not to mention that this card gets stronger as more and more spells are created for the game.
To properly balance the card, I think you'd have to add an additional restriction to the ability. For instance, having it affect only spells of your mark (or opponent's mark, or both) or an element of your choice (though zanz has been giving such cards a wide berth due to slowing the game down with choices) or else pick an element or two that are diametrically opposed to darkness. (i.e. light spells and/or life spells only)
With a restriction something like one of those, I'd absolutely love to have this card, as control style decks are my favourites
In its current game, I'd break it as bad as shards of sacrifice/focus were when they were 'other' cards.