Compelling Deterrence

Return target nonland permanent to its owner's hand. Then that player discards a card if you control a Zombie.

Merrow Commerce

At the beginning of your end step, untap all Merfolk you control.

Synchronous Sliver

Thrumming Hivepool

Affinity for Slivers (This spell costs {1} less to cast for each Sliver you control.)
Slivers you control have double strike and haste.
At the beginning of your upkeep, create two 1/1 colorless Sliver creature tokens.

Herald of Hoofbeats

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
Other Knights you control have horsemanship.

Spell Stutter

Counter target spell unless its controller pays {2} plus an additional {1} for each Faerie you control.

Galerider Sliver

Sliver creatures you control have flying.

Lothlórien Blade

Whenever equipped creature attacks, it deals damage equal to its power to target creature defending player controls.
Equip Elf {2}
Equip {5}

Rooftop Storm

You may pay {0} rather than pay the mana cost for Zombie creature spells you cast.

Scion of Oona

Flash
Flying
Other Faerie creatures you control get +1/+1.
Other Faeries you control have shroud. (They can't be the targets of spells or abilities.)

Diffusion Sliver

Whenever a Sliver creature you control becomes the target of a spell or ability an opponent controls, counter that spell or ability unless its controller pays {2}.

Shifting Sliver

Slivers can't be blocked except by Slivers.

Aquitect's Will

Put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. If you control a Merfolk, draw a card.

Attuma, Atlantean Warlord

Other Merfolk you control get +1/+1.
Whenever one or more Merfolk you control attack a player, draw a card.

Master of the Pearl Trident

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

Stonybrook Banneret

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Merfolk spells and Wizard spells you cast cost {1} less to cast.

Mistform Ultimus

Mistform Ultimus is every creature type (even if this card isn't on the battlefield).