Lord of Atlantis

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

Bog Wraith

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)

Counterspell

Swamp

Flying Men

Black Knight

First strike (This creature deals combat damage before creatures without first strike.)
Protection from white (This creature can't be blocked, targeted, dealt damage, or enchanted by anything white.)

Blue Elemental Blast

Choose one —
• Counter target red spell.
• Destroy target red permanent.

Wall of Spears

Defender (This creature can't attack.)
First strike

Black Lotus

{T}, Sacrifice Black Lotus: Add three mana of any one color.

Unholy Strength

Enchant creature
Enchanted creature gets +2/+1.

Twiddle

You may tap or untap target artifact, creature, or land.

Merfolk of the Pearl Trident

Psychic Venom

Enchant land
Whenever enchanted land becomes tapped, Psychic Venom deals 2 damage to that land's controller.

Underground Sea

Strip Mine

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

Demonic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Volcanic Eruption

Destroy X target Mountains. Volcanic Eruption deals damage to each creature and each player equal to the number of Mountains put into a graveyard this way.

Sinkhole

Mox Sapphire

Weakness

Enchant creature
Enchanted creature gets -2/-1.

Mox Jet

Terror

Destroy target nonartifact, nonblack creature. It can't be regenerated.

Timetwister

Each player shuffles their hand and graveyard into their library, then draws seven cards. (Then put Timetwister into its owner's graveyard.)

Paralyze

Enchant creature
When Paralyze enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
At the beginning of the upkeep of enchanted creature's controller, that player may pay {4}. If the player does, untap the creature.