I came up with the idea for this slight rules modification a while ago but haven't had the chance to playtest it yet. Basically, the idea is to make all effects that would be decided by the d12 controlled directly by the players instead. The main reason to do this is to allow for more strategy and prevent randomness from having as great of an effect on games.
Here's how it works: each time a spell would involve an effects roll, that roll is cancelled and the player instead receives 6 Effect Points. Each player keeps track of their Effect Points (similarly to Health, Mana, etc.). Whenever a player receives Effect Points, the player may invest them (along with any stored Effect Points) into the effects roll on the spell being played. After the player has declared how many Effect Points he/she is investing into the spell, the opposing player may also invest their own Effect Points into the spell as a negative value (similar to how the Tough trait works). The effect listed on the spell corresponding to the total number of Effect Points, if any, is then carried out. Regardless of outcome, all Effect Points invested into the spell are not returned to players.
By the end of the damage & effects step, each player may only possess up to 12 Effect Points. Any points gained beyond that limit are lost. If there are more than two players in a match, only the player who controls the spell involving an effects roll and the opponent targeted by that spell (if any) are allowed to invest Effect Points into that spell. The spell [mwcard=MWSTX2FFA01]Devil's Trident[/mwcard] has its Cripple&Burn and Burn effects reversed (it now takes 9+ points to both Cripple and Burn an enemy). If applicable, damage is always rolled and applied before effects are determined. If the target of the spell dies due to this damage, the effect step is skipped but the player still gains 6 Effect Points.
Ex. Player 1 casts [mwcard=FWA01]Arc Lightning[/mwcard] at Player 2. Player 1 possessed 8 stored Effect Points and immediately gains 6 more for a total of 14 Effect Points. Player 2 possesses 4 Effect Points, and is wearing [mwcard=MWSTX1CKQ03]Colossus Belt[/mwcard]. Player 1 declares that he is investing 12 Effect Points into the spell. Player 2 then announces that he is investing 2 Effect Points into the spell, which adds up to a negative score of 4. 12 - 4 = 8 The final score is 8, so Player 2 is Dazed but not Stunned. Player 1 and 2 now both possess 2 Effect Points each.
Feedback and thoughts are appreciated.