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

{T}: Add {C}. {1}, {T}, Sacrifice this land: Destroy target nonbasic land. Activate only if an opponent controls four or more lands.

Flash Other Merfolk you control get +1/+1. Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

Enchant creature Enchanted creature loses all abilities and is a Toy artifact creature with base power and toughness 0/2 in addition to its other types. As long as enchanted creature is face down, it can't be turned face up.

Svyelun has indestructible as long as you control at least two other Merfolk. Whenever Svyelun attacks, draw a card. Other Merfolk you control have ward {1}. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

Nonbasic lands are Islands.

Kicker {1} (You may pay an additional {1} as you cast this spell.) When this creature enters, if it was kicked, target land becomes an Island for as long as this creature remains on the battlefield. This creature gets +1/+1 as long as an opponent controls an Island.