The Card Itself
Let’s break down the card:
Jace's low converted mana cost is one of his best features. He can can come down turns one or two and begin filtering our draws, but also be cast midgame safely leaving up mana for answers as needed. Casting him late game at four or six mana late game is often still worth it given the full graveyards at that point in the game.
Not relevant for our purposes. We're not Azami, and we don’t want to dilute out Island mana base with cards like Cavern of Souls.
Jace is extremely wimpy. No power is unfortunate given Hidden Strings is a card, and as for blocking, he can block some dorks, more or less, and not much else.
- Tap: Draw a card, then discard a card. If there are five or more cards in your graveyard, exile Jace, Vryn's Prodigy, then return him to the battlefield transformed under his owner's control.
Merfolk Looter, with a twist. This is the bread and butter ability of Jace that you'll use almost every game. Note that this is all one ability, so the transform will happen on resolution, not just because you have five or more cards in your graveyard.
Once he's transformed into Jace, Telepath Unbound (five loyalty counters), we have the following set of abilities:
- +1:Up to one target creature gets -2/-0 until your next turn.
Decreases the power of attackers. Rarely relevant, mostly just there for ticking him up as needed. "Up To" is important: if there are no creatures around, tick up Jace anyhow.
- -3:You may cast target instant or sorcery card from your graveyard this turn. If that card would be put into your graveyard this turn, exile it instead.
This is the juicy bit - a Snapcaster Mage, and what we're using almost always using Jace for as soon as he flips.
- -9: You get an emblem with "Whenever you cast a spell, target opponent puts the top five cards of his or her library into his or her graveyard."
We essentially never use this, as by the time we have three or more loyalty, we'd prefer to use his -3 again.
Jace's Role In The Deck
Jace, Vryn's Prodigy
's roles in this deck are fairly diverse, though it's mostly along the line of a Merfolk Looter stapled to a Snapcaster Mage.
His primary ability is as a looter in the command zone. This allows us to filter our hand, dig deeper into our topdeck, and fill up our graveyard for Snapcaster Mage and Jace's minus three planeswalker ability. Instants and Sorceries aren't "gone" with the discard given the minus three, so don't be afraid to pitch hefty pay-off cards like Enter the Infinite early game to dig for more relevant cards. In some grindy, slower games I'm often been quite cautious about filling up my graveyard, given Jace's flashback is usually a one-off (and smart opponents will keep Jace from ever getting enough loyalty to use it again with small-scale beats). That being said, letting him flip for value plays is fine if there's no alternative or route to combo.
While he isn't an infinite outlet in a traditional sense, you can use the Isochron Scepter/Dramatic Reversal/mana rocks combo to loot your deck and filter your hand into a winning hand, or even just flashback something relevant. It gets riskier if you have no hand and need to flashback a wheel, and even riskier if you only have infinite untaps and not infinite mana (i.e. two mana's worth of mana rocks), but is usually a winning play nonetheless.
Once Jace flips, we're almost always using his minus three that turn. Given the deck's heavy focus on High Tide, that card is easily the most common target (for the double High Tide effect), but it's far from the only one, and there are many scenarios where double High Tide is either unnecessary or even a poor choice (e.g. Tide but no draw in hand, but there's a Time Spiral in the graveyard). If you have everything you need to win in hand off a single Tide, consider giving a counterspell flashback. A Paradox Engine in play has made me double-cast Fabricate for the win. While Tide is the deck's focus, it's important to not get tunnel vision about that card and Jace's minus three. The correct target is contextual.
Sadly, in this format, Jace's plus one is not fantastic except for ticking up for another minus three and denying Tymna draws. Still, it's worth keeping in mind if there are relevant targets like Tymna or Brago. We can't effectively defend Jace given our low creature count, and usually aren't sad to see him removed due to the gaining the ability to recast him and then get a looter and flashback again.
Jace's ultimate could, theoretically, be a win condition, but in hundreds of games on Jace, that scenario hasn’t happened. Given situations as odd as victory via Palinchron beatdown and storming off via an opponent's High Tide have happened, that's saying something. For almost all games, it might as well not be on the card. (Much like Teferi, Temporal Archmage's ultimate in his deck).
