Lord of Atlantis

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

Island

Psionic Blast deals 4 damage to any target and 2 damage to you.

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

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

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

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

{T}: Add {U}.
{T}: Target creature loses banding and all "bands with other" abilities until end of turn. Activate only during any upkeep step.