Stormtide Leviathan — ruling 1

Stormtide Leviathan's second ability causes each land on the battlefield to have the land type Island. Each land thus has the ability "{T}: Add {U}." Nothing else changes about those lands, including their names, other subtypes, other abilities, and whether they're legendary or basic.

Stormtide Leviathan — ruling 2

If Stormtide Leviathan loses its abilities, all lands on the battlefield (including those that enter the battlefield later on) will still be Islands in addition to their other types and will still be able to tap to produce {U}. The way continuous effects work, Stormtide Leviathan's type-changing ability is applied before the effect that removes that ability is applied.

Stormtide Leviathan — ruling 3

Stormtide Leviathan's third ability affects all creatures with neither flying nor islandwalk, regardless of who controls them. They can't attack any player or planeswalker.

Stormtide Leviathan — ruling 4

Islandwalk cares about lands with the land type Island, not necessarily lands named Island.

Stormtide Leviathan : règles, fonctionnement et interactions (MTG)

Stormtide Leviathan is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Islandwalk (This creature can't be blocked as long as defending player controls an Island.) All lands are Islands in addition to their other types. Creatures without flying or islandwalk can't attack.

Complete guide

Stormtide Leviathan is a massive blue creature that dictates the flow of the entire battlefield by turning the ground into an ocean. By transforming every land into an Island and grounding non-aquatic attackers, it forces your opponents to play by your rules. This behemoth is a finisher that provides both a powerful clock and a formidable defense.

Flooding the Field

Stormtide Leviathan has a continuous effect that adds the 'Island' subtype to every land on the battlefield. This doesn't replace their existing types; instead, they become Islands in addition to being Forests, Swamps, or even legendary lands. Because they are now Islands, every land gains the intrinsic mana ability to tap for blue mana, though they retain all their original names and abilities.

The Kraken's Edict

While this creature is on the battlefield, combat becomes restricted. Any creature that lacks the flying keyword or the islandwalk keyword is physically unable to be declared as an attacker. This affects all players equally, meaning your own ground-based creatures will also be stuck on the shore unless they have a way to fly or swim through the newly formed sea.

Layering and Interaction

A common point of confusion involves what happens if Stormtide Leviathan loses its abilities, perhaps through an opponent's spell. Due to Magic's layer system, the type-changing effect (Layer 4) is applied before abilities are removed (Layer 6). This means even if the Leviathan is silenced, the lands remain Islands. However, the restriction on attacking and the islandwalk ability would cease to function if the Leviathan loses its abilities.

Strategic Deployment

You should play Stormtide Leviathan when you need to stabilize a board against aggressive ground-based decks. Since it turns your opponent's lands into Islands, its own islandwalk ability ensures that it can't be blocked, providing an unblockable 8/8 body to close out the game quickly while the opponent's army is unable to strike back.

Interaction examples

Taking to the Skies

Thought Monitor

With Stormtide Leviathan on the battlefield, most creatures are grounded. However, because Thought Monitor has flying, it ignores the Leviathan's restriction and can be declared as an attacker normally. Additionally, all your artifacts that provide mana will still function, while your lands now provide blue mana to help cast more spells.

Controlling the Tides

Hullbreaker Horror

If you have both creatures out, your opponent is in a difficult position. Hullbreaker Horror does not have flying or islandwalk, so it cannot attack while Stormtide Leviathan is present. However, the Horror can still use its Flash ability to enter the battlefield and its triggered ability to bounce threats back to the opponent's hand, keeping the board clear while the Leviathan swings for lethal damage.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Stormtide Leviathan

Original English text — Wizards of the Coast / Scryfall

#1July 18, 2014· Wizards of the Coast
Stormtide Leviathan's second ability causes each land on the battlefield to have the land type Island. Each land thus has the ability ": Add ." Nothing else changes about those lands, including their names, other subtypes, other abilities, and whether they're legendary or basic.
No other card is named in this ruling.
#2July 18, 2014· Wizards of the Coast
If Stormtide Leviathan loses its abilities, all lands on the battlefield (including those that enter the battlefield later on) will still be Islands in addition to their other types and will still be able to tap to produce . The way continuous effects work, Stormtide Leviathan's type-changing ability is applied before the effect that removes that ability is applied.
No other card is named in this ruling.
#3July 18, 2014· Wizards of the Coast
Stormtide Leviathan's third ability affects all creatures with neither flying nor islandwalk, regardless of who controls them. They can't attack any player or planeswalker.
No other card is named in this ruling.
#4July 18, 2014· Wizards of the Coast
Islandwalk cares about lands with the land type Island, not necessarily lands named Island.
No other card is named in this ruling.