As written, exhaust abilities are abilities that can only be activated once per game, meaning once they are used, that's it, unless the card is recast at a later point in the game
The good part about Discovery / Dispersal is that its good early and late in the game, and you can cast it with blue or black mana
The problem is that the card that would have been sold fractionally on Liquid Marketplace and at auction would be the same
But this card has a few tricks up its sleeve
Well, lets just say that Mind Twist would likely be the more popular choice, assuming you could only pick one
It reads, Whenever a player plays a spell that counters a spell that has been played or a player plays a spell that comes into play with counters, that player may counter the next spell played or put an additional counter on a permanent that has already been played, but not countered. Although its obviously tongue in cheek, I appreciate this card as an admission statement, or rather, a concession against the inevitability of using unclear language in the game