Control Magic

Enchant creature
You control enchanted 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.

Merfolk of the Pearl Trident

Counterspell

Island

Sol Ring

Clone

You may have Clone enter as a copy of any creature on the battlefield.

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.

Lord of Atlantis

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

Serendib Efreet

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