I think Jace has some of the most powerful combos in the game, that need to be nerfed a bit. I run a jace mana deny deck (yes, I am that evil), with several combos that lock down other decks. It is not his first ability that crazy, but his second.
Here is my current deck:
Sphinx’s Tutelage - Jehessian Thief - Jaces Sanctum: Jaces Sanctum drains 3, Sphinx’s Tutelage raises cost by 2, then Jehessian Thief draws a card and Sphinx’s Tutelage activates again for another raise in cost by 2. In total, 3 drain + 4 increase in cost.
Willbreaker - Foundry of the Consuls - Jace’s Second ability: Foundry is nice the first time, but so much nicer for Free the second/ third/fourth time, and with Willbreaker, I snag an enemy creature for a round when I play this. I use their creatures to increase my damage, since it is pretty low.
Mizzium Meddler - Harbringer of Tides: These are my get out of jail free cards. All decks like time, and this deck needs it. Mizzium actually messes up my first combo, so I don’t cast him when it is up (does not matter, I draw 2 cards a turn so I ditch him), but if I get hit with board clear or a rough draw this guy buys me time. Harbringer bounces a creature as soon as it lands, and raises cost.
And my last 3 cards
Sigil of Valor - Throwing Knife - Helm of the Gods: That makes 4 total supports in the deck with decient staying power and not to expensive costs, so I can usually get the Helm to activate. I have no defense cards, since I want to do straight damage as fast as possible, and The Helm makes sure a reach or defender goes down before they are a problem. Also with card draw, Helm is easily pitched. Unfortunatly, Helm does not work with Jace’s second ability, it actually takes away the buff from the creature and then you can re-apply it, but that can help if you need to move the buff and activate Willbreaker if it is out.
It draws pretty well, since half of my cards are effectively creatures that either build combos or delay for time to build them. Two of the supports also delay for time as well as Jace’s first ability for a little bit. Blue is very strong, and pretty slow, a game balance for a game that rewards speed over win percentage (I float at 95%, but I play all 5 decks so I can’t say my exact win percentage for this deck.)
To balance this better, and to bring the win percentage down of for almost all decks, you just have to let the game randomly choose if the player or the opponent goes first. This deck relies on getting 1 card out before the opponent can, setting the tempo. Since you always go first, I can always get at least 4 mana on my first card. Typically I’ll get even more since it is a clean board. Without that, this deck would suffer greatly, and would need some adjustment with some cheeper cards in the mix.