Watery Grave

({T}: Add {U} or {B}.)
As Watery Grave enters, you may pay 2 life. If you don't, it enters tapped.

Isareth the Awakener

Deathtouch
Whenever Isareth the Awakener attacks, you may pay {X}. When you do, return target creature card with mana value X from your graveyard to the battlefield with a corpse counter on it. If that creature would leave the battlefield, exile it instead of putting it anywhere else.

Jace, Cunning Castaway

+1: Whenever one or more creatures you control deal combat damage to a player this turn, draw a card, then discard a card.
−2: Create a 2/2 blue Illusion creature token with "When this creature becomes the target of a spell, sacrifice it."
−5: Create two tokens that are copies of Jace, Cunning Castaway, except they're not legendary.

Karn, Scion of Urza

+1: Reveal the top two cards of your library. An opponent chooses one of them. Put that card into your hand and exile the other with a silver counter on it.
−1: Put a card you own with a silver counter on it from exile into your hand.
−2: Create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control."

Siren Stormtamer

Flying
{U}, Sacrifice Siren Stormtamer: Counter target spell or ability that targets you or a creature you control.

Island

Pilfering Imp

Flying
{1}{B}, {T}, Sacrifice Pilfering Imp: Target opponent reveals their hand. You choose a nonland card from it. That player discards that card. Activate only as a sorcery.

Nightveil Sprite

Flying
Whenever Nightveil Sprite attacks, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Chart a Course

Draw two cards. Then discard a card unless you attacked this turn.

Dive Down

Target creature you control gets +0/+3 and gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Plaguecrafter

When Plaguecrafter enters, each player sacrifices a creature or planeswalker of their choice. Each player who can't discards a card.

Swamp

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Thief of Sanity

Flying
Whenever Thief of Sanity deals combat damage to a player, look at the top three cards of that player's library, exile one of them face down, then put the rest into their graveyard. You may cast that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.

Unmoored Ego

Choose a card name. Search target opponent's graveyard, hand, and library for up to four cards with that name and exile them. That player shuffles, then draws a card for each card exiled from their hand this way.

Curious Obsession

Enchant creature
Enchanted creature gets +1/+1 and has "Whenever this creature deals combat damage to a player, you may draw a card."
At the beginning of your end step, if you didn't attack with a creature this turn, sacrifice Curious Obsession.

Negate

Drowned Catacomb

Drowned Catacomb enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Warkite Marauder

Flying
Whenever Warkite Marauder attacks, target creature defending player controls loses all abilities and has base power and toughness 0/1 until end of turn.

Admiral's Order

Raid — If you attacked this turn, you may pay {U} rather than pay this spell's mana cost.
Counter target spell.

Cast Down

Kitesail Freebooter

Flying
When Kitesail Freebooter enters, target opponent reveals their hand. You choose a noncreature, nonland card from it. Exile that card until Kitesail Freebooter leaves the battlefield.