Cool Card Design of the Day
5/4/2016 - Ravenous Tsunami inverts Islandhome/Islandwalk like Lonely Serpent so that it's good against most decks and a liability against some (rather than weak against most and good against some / irrelevant against most decks and absurd against some).
Like Hungry Serpent, Ravenous Tsunami uses must-attack rather than can't-attack. There's an argument for using must-attack when it's thematic in blue, given red and blue's shared history of sirens, but I'm 100% fine with just making this red (though red hating mountains seems wrong, and red hating islands seems archaic).
All that adds up to a creature that fills the role of a set's sea serpent, but is different enough it wants another creature type. Ravenous Tsunami is uncommon because there's very little downside to this 5/5 for six.