Unsummon

Return target creature to its owner's hand.

Psychic Purge

Psychic Purge deals 1 damage to any target.
When a spell or ability an opponent controls causes you to discard Psychic Purge, that player loses 5 life.

Ancestral Recall

Blood Moon

River Merfolk

{U}: River Merfolk gains mountainwalk until end of turn. (It can't be blocked as long as defending player controls a Mountain.)

Mishra's Factory

{T}: Add {C}.
{1}: Mishra's Factory 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.

Lord of Atlantis

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

Volcanic Island

Energy Flux

All artifacts have "At the beginning of your upkeep, sacrifice this artifact unless you pay {2}."

Serendib Efreet

Flying
At the beginning of your upkeep, Serendib Efreet deals 1 damage to you.

Merfolk of the Pearl Trident

Chaos Orb

{1}, {T}: If Chaos Orb is on the battlefield, flip Chaos Orb onto the battlefield from a height of at least one foot. If Chaos Orb turns over completely at least once during the flip, destroy all nontoken permanents it touches. Then destroy Chaos Orb.

Time Walk

Strip Mine

{T}: Add {C}.
{T}, Sacrifice Strip Mine: Destroy target land.

Counterspell

Island

Flying Men

Aeolipile

{1}, {T}, Sacrifice Aeolipile: It deals 2 damage to any target.

Desert

{T}: Add {C}.
{T}: Desert deals 1 damage to target attacking creature. Activate only during the end of combat step.

Force Spike

Counter target spell unless its controller pays {1}.

Pendelhaven

{T}: Add {G}.
{T}: Target 1/1 creature gets +1/+2 until end of turn.

Falling Star

Flip Falling Star onto the playing area from a height of at least one foot. Falling Star deals 3 damage to each creature it lands on. Tap all creatures dealt damage by Falling Star. If Falling Star doesn't turn completely over at least once during the flip, it has no effect.