Illdus, Omen of the Depths

At the beginning of your upkeep you get an
emblem with: "Leviathan, Serpent, Kraken,
Octopus, and Crab spells you cast cost {1} less
to cast."
Leviathans, Serpents, Krakens, Octopuses,
and Crabs you control have islandwalk.