Logic Knot

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Counter target spell unless its controller pays {X}.

Mesmeric Sliver

All Slivers have "When this permanent enters, you may fateseal 1." (To fateseal 1, its controller looks at the top card of an opponent's library, then they may put that card on the bottom of that library.)

Narcomoeba

Flying
When this card is put into your graveyard from your library, you may put it onto the battlefield.

Counter target spell if no mana was spent to cast it.

Sarcomite Myr

{2}: This creature gains flying until end of turn.
{2}, Sacrifice this creature: Draw a card.

Second Wind

Enchant creature
{T}: Tap enchanted creature.
{T}: Untap enchanted creature.

Shapeshifter's Marrow

At the beginning of each opponent's upkeep, that player reveals the top card of their library. If it's a creature card, the player puts the card into their graveyard and this enchantment becomes a copy of that card. (If it does, it loses this ability.)

Spellweaver Volute

Enchant instant card in a graveyard
Whenever you cast a sorcery spell, copy the enchanted instant card. You may cast the copy without paying its mana cost. If you do, exile the enchanted card and attach this Aura to another instant card in a graveyard.

Even the Odds

Soldier

Cast this spell only if you control fewer creatures than each opponent.
Create three 1/1 white Soldier creature tokens.

Spin into Myth

Put target creature on top of its owner's library, then fateseal 2. (To fateseal 2, look at the top two cards of an opponent's library, then put any number of them on the bottom of that player's library and the rest on top in any order.)

Vedalken Aethermage

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, return target Sliver to its owner's hand.
Wizardcycling {3} ({3}, Discard this card: Search your library for a Wizard card, reveal it, put it into your hand, then shuffle.)

Whip-Spine Drake

Morph

Flying
Morph {2}{W} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Augur of Skulls

{1}{B}: Regenerate this creature.
Sacrifice this creature: Target player discards two cards. Activate only during your upkeep.

Cutthroat il-Dal

Hellbent — This creature has shadow as long as you have no cards in hand. (It can block or be blocked by only creatures with shadow.)

Festering March

Creatures your opponents control get -1/-1 until end of turn. Exile Festering March with three time counters on it.
Suspend 3—{2}{B} (Rather than cast this card from your hand, you may pay {2}{B} and exile it with three time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)

Gibbering Descent

At the beginning of each player's upkeep, that player loses 1 life and discards a card.
Hellbent — Skip your upkeep step if you have no cards in hand.
Madness {2}{B}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Future Sight