Icewrought Sentry

Vigilance
Whenever Icewrought Sentry attacks, you may pay {1}{U}. When you do, tap target creature an opponent controls.
Whenever you tap an untapped creature an opponent controls, Icewrought Sentry gets +2/+1 until end of turn.

Island

Snaremaster Sprite

Flying
When Snaremaster Sprite enters the battlefield, you may pay {2}. When you do, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Agatha's Soul Cauldron

You may spend mana as though it were mana of any color to activate abilities of creatures you control.
Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron.
{T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.

Mocking Sprite

Flying
Instant and sorcery spells you cast cost {1} less to cast.

Archive Dragon

Flying
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
When Archive Dragon enters the battlefield, scry 2.

Bitter Chill

Enchant creature
When Bitter Chill enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
When Bitter Chill is put into a graveyard from the battlefield, you may pay {1}. If you do, scry 1, then draw a card.

Counterbalance

Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, counter that spell if it has the same mana value as the revealed card.

Hatching Plans

When Hatching Plans is put into a graveyard from the battlefield, draw three cards.

As Foretold

At the beginning of your upkeep, put a time counter on As Foretold.
Once each turn, you may pay {0} rather than pay the mana cost for a spell you cast with mana value X or less, where X is the number of time counters on As Foretold.

Gadwick's First Duel

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Create a Cursed Role token attached to up to one target creature. (If you control another Role on it, put that one into the graveyard. Enchanted creature is 1/1.)
II — Scry 2.
III — When you next cast an instant or sorcery spell with mana value 3 or less this turn, copy that spell. You may choose new targets for the copy.

Hylda's Crown of Winter

{1}, {T}: Tap target creature. This ability costs {1} less to activate during your turn.
{3}, Sacrifice Hylda's Crown of Winter: Draw a card for each tapped creature your opponents control.

Ice Out

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.)
This spell costs {1} less to cast if it's bargained.
Counter target spell.

Throne of Eldraine

As Throne of Eldraine enters the battlefield, choose a color.
{T}: Add four mana of the chosen color. Spend this mana only to cast monocolored spells of that color.
{3}, {T}: Draw two cards. Spend only mana of the chosen color to activate this ability.

Johann's Stopgap

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.)
This spell costs {2} less to cast if it's bargained.
Return target nonland permanent to its owner's hand. Draw a card.

Splashy Spellcaster

Whenever you cast an instant or sorcery spell, create a Sorcerer Role token attached to up to one other target creature you control. (If you control another Role on it, put that one into the graveyard. Enchanted creature gets +1/+1 and has "Whenever this creature attacks, scry 1.")

Succumb to the Cold

Tap one or two target creatures an opponent controls. Put a stun counter on each of them. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Crystal Grotto

When Crystal Grotto enters the battlefield, scry 1.
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Tenacious Tomeseeker

Bargain (You may sacrifice an artifact, enchantment, or token as you cast this spell.)
When Tenacious Tomeseeker enters the battlefield, if it was bargained, return target instant or sorcery card from your graveyard to your hand.

Freeze in Place

Tap target creature an opponent controls and put three stun counters on it. Scry 2. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Eldrazi Conscription

Enchant creature
Enchanted creature gets +10/+10 and has trample and annihilator 2. (Whenever it attacks, defending player sacrifices two permanents.)

Living Lectern

{1}, Sacrifice Living Lectern: Draw a card. Create a Sorcerer Role token attached to up to one other target creature you control. Activate only as a sorcery. (If you control another Role on it, put that one into the graveyard. Enchanted creature gets +1/+1 and has "Whenever this creature attacks, scry 1.")