Vadrok's ability is only valuable if you already have cards in graveyard that she can cast. To fill your graveyard, the best effects are spells like
Frantic Search and
Cathartic Reunion, which let you dig while also pitching relevant spells into graveyard. However, we also run effects such as
Winds of Rebuke, which fill the graveyard in more haphazard ways, as well as more general wheel effects (
Wheel of Fortune and
Windfall).
In this deck, it's good to burn your removal spells early and often, to gain tempo. If you can shoot a low-CMC commander with
Pongify in the early game, it's often a good idea -- since Vadrok's mutation trigger will let you cast the removal spell a second time, for additional advantage. Moreover, this is the only deck where it's plausible to cast
Narset, Parter of Veils or
Dack Fayden without any protection on battlefield -- even if you only get to activate their abilities once or twice, when they die you can recast them with full loyalty.
More detailed explanations are given below:
Frantic Search and
Snap: These are by far the best two cards to recast from graveyard, because they recoup mana when we cast them for free -- this makes our mutations effectively cost 2-3 less mana, while also generating advantage and holding up mana for interaction. Also, they allow us to effectively "chain" mutate creatures together, triggering Vadrok three or four times in a single turn for massive advantage -- remember that when a creature mutates, ALL of its mutation abilities are put on the stack again, including Vadrok's own recast trigger.
Curator's Ward: This allows Vadrok to "enter" with additional protection, and will draw cards when Vadrok leaves battlefield (helping to avert the normal 2-for-1 when Vadrok dies). This is especially good when Vadrok is mutated onto something menacing like
Markov Blademaster, or something small and vulnerable like
Cephalid Constable or
Surrakar Spellblade.
Jeskai Ascendancy and
Sevinne's Reclamation: These two cards are included in the deck for the explicit purpose of casting them from graveyard. We can abuse Reclamation in particular, by getting its "double" mode with each mutation trigger... and
Jeskai Ascendancy is a critical piece in many of our combos (as well as giving Vadrok prowess and "vigilance".
Mystic Remora and
Rhystic Study: You've never seen your opponents cry until you recur these multiple times in the same game, ignoring removal.
Mystic Remora can also be sacrificed when its upkeep cost grows too high, then recurred for free with zero counters again.
Underworld Breach: Oddly, Breach is less good than one might expect, when recurred off of a mutation trigger. It's hard to both mutate AND hold up the necessary amount of mana to go off with Breach. Still, it's often possible to re-cast Breach from graveyard, then immediately bounce it to your hand with
Chain of Vapor or
Winds of Rebuke, to prepare for the next turn.
Dack Fayden and
Narset, Parter of Veils: Our deck doesn't care too much when either of these planeswalkers die, because we can recast them easily with Vadrok's ability. In particular, Dack often comes down T3, steals an artifact, then dies... at which point we can recast him at a full three loyalty and immediately steal a *second* thing! My opponents have learned that it's often more dangerous to kill Dack than leave him alive at 1 loyalty.
Cathartic Reunion,
Chart a Course,
Faithless Looting,
Impulse: These are simple sources of card advantage when cast from graveyard. Simple, solid, effective. They are the bread and butter of this list -- helping fill our hand and graveyard in the early game, still useful in a pinch when recast off of Vadrok's trigger.
Gamble: This can be very context-dependent, but the discard effect is rarely as bad as one might expect, since we can recast most of the nonland cards in this deck from graveyard. In particular,
Gambleing for
Frantic Search is a win-win, whether we discard it or not.
Merchant Scroll: This lets us tutor for
Snap or a solid counterspell (often
Fierce Guardianship or
Force of Will), ensuring that we have protection for Vadrok in hand. And as mentioned above,
Frantic Search is *monstrously* good in this list, both as part of our combo lines and as general value and mana ramp when mutating with Vadrok.
Mystical Tutor can also do something similar, though unfortunately it does not gain card advantage in the same way.
Wheel of Fortune and
Windfall: These can be fine when recast off Vadrok, especially if we control
Narset, Parter of Veils or
Consecrated Sphinx. But be cautious about recasting these, as someone will usually find removal for Vadrok in their new hand.
Abrade,
Pongify,
Rapid Hybridization,
Reality Shift: It's always helpful to cast removal off our commander, making her into a
Ravenous Chupacabra as she enters. Plus, all of these options can also kill troublesome blockers, letting her swing unopposed.
Normally, we cannot cast counterspells off of Vadrok's recursion trigger. However,
Sea-Dasher Octopus or
Pouncing Shoreshark can allow us to cast counterspells or
Deflecting Swat at instant speed with Vadrok's trigger, acting as additional "counterspells" when necessary.