Sturmtief-Leviathan {5}{U}{U}{U}

Kreatur — Leviathan

Inseltarnung (Diese Kreatur kann nicht geblockt werden, solange der verteidigende Spieler eine Insel kontrolliert.)

Alle Länder sind zusätzlich zu ihren sonstigen Typen Inseln.

Kreaturen ohne Flugfähigkeit oder Inseltarnung können nicht angreifen.

8/8

Illustrated by Karl Kopinski

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Only the English version of a Magic card receives Oracle updates and errata. View this card in English. (Scryfall note)
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. (2014-07-18)
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. (2014-07-18)

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. (2014-07-18)
Islandwalk cares about lands with the land type Island, not necessarily lands named Island. (2014-07-18)