: Draw a card, then discard a card. If there are five or more cards in your graveyard, exile Jace, then return him to the battlefield transformed under his owner's control.
+1: Up to one target creature gets -2/-0 until your next turn.
−3: You may cast target instant or sorcery card from your graveyard this turn. If that spell would be put into your graveyard, exile it instead.
−9: You get an emblem with "Whenever you cast a spell, target opponent mills five cards."
Mono-blue self-mill and card advantage that flips Jace into a planeswalker, then leverages instants/sorceries from the graveyard to grind value, protect yourself, and combo off. You loot to fill the graveyard early, flip Jace, and use his -3 to recast key spells while building toward a control or combo finish.
Cheap two-mana commander that provides repeatable card filtering and graveyard fuel
Flips into a planeswalker that recasts spells from the graveyard, generating huge value
Mono-blue gives access to the best counterspells, card draw, and interaction in the format
Enables graveyard-matters and spellslinger synergies for very little investment
Fragile front side dies to any removal or combat before flipping
Mono-blue struggles with permanent-based threats and lacks efficient creature/enchantment removal
Self-mill can fuel opponents' graveyard hate or mill yourself out if careless
Slow to close games without a dedicated combo or finisher