The List

Calculated Dismissal

Calculated Dismissal {2}{U}

Instant
Counter target spell unless its controller pays {3}.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, scry 2.
Day's Undoing

Day's Undoing {2}{U}

Sorcery
Each player shuffles their hand and graveyard into their library, then draws seven cards. If it's your turn, end the turn.
Dreadwaters

Dreadwaters {3}{U}

Sorcery
Target player mills X cards, where X is the number of lands you control.
Stray into the Morkrut and it may rise to claim you.
Aven Battle Priest

Aven Battle Priest {5}{W}

Creature - Bird Cleric
Flying
When this creature enters, you gain 3 life.
When the shadow of the aven falls across the battlefield, hope rises in the hearts of the soldiers.
3/3
Jace, Vryn's Prodigy
Jace, Telepath Unbound

Jace, Vryn's Prodigy {1}{U}

Legendary Creature - Human Wizard
{T}: 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.
"People's thoughts just come to me. Sometimes I don't know if it's them or me thinking."
0/2
Card has other part: Jace, Telepath Unbound
Jace, Telepath Unbound
Jace, Vryn's Prodigy

Jace, Telepath Unbound

Legendary Planeswalker - Jace
(Color indicator: Jace, Telepath Unbound is blue)
[+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."
Loyalty:
5
Card has other part: Jace, Vryn's Prodigy
Ringwarden Owl

Ringwarden Owl {3}{U}{U}

Creature - Bird
Flying
Prowess
The owls learn of mana from the mages who know it best.
3/3
Blessed Spirits

Blessed Spirits {2}{W}

Creature - Spirit
Flying
Whenever you cast an enchantment spell, put a +1/+1 counter on this creature.
Not all heroes die in armor.
2/2
Send to Sleep

Send to Sleep {1}{U}

Instant
Tap up to two target creatures.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, those creatures don't untap during their controllers' next untap steps.
Sigiled Starfish

Sigiled Starfish {1}{U}

Creature - Starfish
{T}: Scry 1.
Kruphix hid the most dire prophecies about humankind where humans would never find them and tritons wouldn't care to read them.
0/3
Related cards: Oyaminartok, Polar Werebear Tireless Angler
Skaab Goliath

Skaab Goliath {5}{U}

Creature - Zombie Giant
As an additional cost to cast this spell, exile two creature cards from your graveyard.
Trample
Three heads are better than one.
6/9
Sphinx's Tutelage

Sphinx's Tutelage {2}{U}

Enchantment
Whenever you draw a card, target opponent mills two cards. If two nonland cards that share a color were milled this way, repeat this process.
{5}{U}: Draw a card, then discard a card.
"You've never considered the implications of dealing with another telepath, Jace."
Celestial Flare

Celestial Flare {W}{W}

Instant
Target player sacrifices an attacking or blocking creature of their choice.
"You were defeated the moment you declared your aggression."
—Gideon Jura
Whirler Rogue

Whirler Rogue {2}{U}{U}

Creature - Human Rogue Artificer
When this creature enters, create two 1/1 colorless Thopter artifact creature tokens with flying.
Tap two untapped artifacts you control: Target creature can't be blocked this turn.
2/2
Catacomb Slug

Catacomb Slug {4}{B}

Creature - Slug
"The entire murder scene was covered in dripping, oozing slime. No need for a soothsayer to solve that one."
—Pel Javya, Wojek investigator
2/6
Dark Dabbling

Dark Dabbling {2}{B}

Instant
Regenerate target creature. Draw a card.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, also regenerate each other creature you control.
Fetid Imp

Fetid Imp {1}{B}

Creature - Imp
Flying
{B}: This creature gains deathtouch until end of turn.
1/2
Pongify

Pongify {U}

Instant
Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.
Some spellcrafting mistakes go on to become spells of their own.
Related card: The Mystical Archive
Brainstealer Dragon

Brainstealer Dragon {5}{B}{B}

Creature - Dragon Horror
Flying
At the beginning of your end step, exile the top card of each opponent's library. You may play those cards for as long as they remain exiled. If you cast a spell this way, you may spend mana as though it were mana of any color to cast it.
Whenever a nonland permanent an opponent owns enters the battlefield under your control, they lose life equal to its mana value.
6/6
Faithless Looting

Faithless Looting {R}

Sorcery
Draw two cards, then discard two cards.
Flashback {2}{R}
Impulsive Pilferer

Impulsive Pilferer {R}

Creature - Goblin Pirate
When this creature dies, create a Treasure token.
Encore {3}{R}
1/1
Storm-Kiln Artist

Storm-Kiln Artist {3}{R}

Creature - Dwarf Shaman
This creature gets +1/+0 for each artifact you control.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a Treasure token.
A captured elemental makes for a potent, albeit unstable, power source.
2/2
Volcanic Torrent

Volcanic Torrent {4}{R}

Sorcery
Cascade
Volcanic Torrent deals X damage to each creature and planeswalker your opponents control, where X is the number of spells you've cast this turn.
Third Path Iconoclast

Third Path Iconoclast {U}{R}

Creature - Human Monk
Whenever you cast a noncreature spell, create a 1/1 colorless Soldier artifact creature token.
"When all you have is a hammer, everything looks like a nail. I merely propose expanding our toolbox."
2/1
Arcane Signet

Arcane Signet {2}

Artifact
{T}: Add one mana of any color in your commander's color identity.
It started as a mere drop of water. The Magic Mirror crystallized it into much more.