Unstable Mutation

Enchant creature
Enchanted creature gets +3/+3.
At the beginning of the upkeep of enchanted creature's controller, put a -1/-1 counter on that creature.

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Sandbar Merfolk

Cycling {2} ({2}, Discard this card: Draw a card.)

Thwart

You may return three Islands you control to their owner's hand rather than pay this spell's mana cost.
Counter target spell.

Tidal Warrior

{T}: Target land becomes an Island until end of turn.

Nevinyrral's Disk

This artifact enters tapped.
{1}, {T}: Destroy all artifacts, creatures, and enchantments.

Boomerang

Return target permanent to its owner's hand.

Hurkyl's Recall

Return all artifacts target player owns to their hand.

Seal of Removal

Sacrifice this enchantment: Return target creature to its owner's hand.

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Seahunter

{3}, {T}: Search your library for a Merfolk permanent card, put it onto the battlefield, then shuffle.

Island

Rootwater Diver

{T}, Sacrifice this creature: Return target artifact card from your graveyard to your hand.

Winter Orb

As long as this artifact is untapped, players can't untap more than one land during their untap steps.

Sapphire Charm

Choose one —
• Target player draws a card at the beginning of the next turn's upkeep.
• Target creature gains flying until end of turn.
• Target creature an opponent controls phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before its controller untaps during their next untap step.)

Waterfront Bouncer

{U}, {T}, Discard a card: Return target creature to its owner's hand.

Mishra's Factory

{T}: Add {C}.
{1}: This land becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land.
{T}: Target Assembly-Worker creature gets +1/+1 until end of turn.

Counterspell

Control Magic

Enchant creature
You control enchanted creature.

Inspiration

Feedback

Enchant enchantment
At the beginning of the upkeep of enchanted enchantment's controller, this Aura deals 1 damage to that player.