Devouring Deep

These common cards don't give you a lot to work with, do they?

This would actually be a good time to talk about something so tangentially related to Devouring Deep that any segue would fail.

Islandhome.

OK, bear with me. I know that a) Legends doesn't support Islandhome; b) Islandhome, as it exists, is a bad ability in the purest sense; and c) the only connection Devouring Deep has to Islandhome is that it's a blue fish. It's closer to Island Fish Jasconius than it is to Sea Serpent.

... but Island Fish Jasconius has Islandhome! Full circle, segue made (though still hardly successful, since it's a segue from the topic at hand back to the topic at hand).

I've often looked at Islandhome as a cool ability in the flavor sense, and it has some neat mechanical implications too. Its execution was poor and its drawback was never capitalized on -- Sea Serpent should have been four mana, for example -- but I think there's something we can grasp onto in the ability.

So here's what I like about the ability:

• It ties into blue's Phantasmal Terrain suite of spells. I've always had a soft spot for this line; I like spells that have both aggressive and structural uses. While the current incarnations only turn lands into islands -- color fixing in blue is perhaps a bridge too far -- they still (typically) turn off nonbasics, attack greedy multicolor decks and, in a pinch, turn your own land into an extra source of blue.
• It's a nice mirror to high-flying, the restriction seen on cards such as Cloud Elemental. Blue and black have a similar take on combat -- they typically don't have very strong or efficient guys, but in their respective domains, they've got a certain amount of supremacy. (In the Brave New World of Magic, that's changing somewhat -- every color is getting strong guys at decent prices now -- but even then, green and white still edge out both colors in ground-pounders and flyers, respectively, in the important mid-range creature suites.) Just as Cloud Elemental trumps most other three-mana flyers -- particularly those at common -- I'd like to see Islandhome as another such take on "I'm supreme in my domain."

What I don't like about the ability:

• Its "you must control an Island" clause is a little silly. In almost every deck that would run one of these guys, Island is going to be a common sight. I'd rather impose a price cut and beef up the blue requirements -- bumping Sea Serpent to 2UU, for example -- to reflect the creature's strong ties to the ocean. Adding heftier colored mana requirements also allows us to give some running cover to our cheated mana costs -- and provides the up-side to a negative ability.
• It requires support. You'll need to give blue a way to make opposing lands watery in every block that these guys exist. That's not so bad -- blue usually gets a Phantasmal Terrain variant in very Standard season -- but it means that the Islandhome creatures will need to be fairly competitive. A situational 5/5 for four mana isn't bad, but it's not going to break any metagames any time soon. For proof, look at Lorwyn-block merfolk. The tribe had strong synergies and could slip through a ton of unblockable damage -- but that required a lot of hoops, including tapping a separate merfolk or two. Wake Thrasher ended up seeing some play as a big blue dude for a little while, but even that eventually was phased out for smarter beats.
• It's purely downside. Why is this important? Because Magic keywords should have implications beyond their initial impact. Take the recent ability undying, for example. There's the obvious usage -- going crazy aggro (or crazy defensive, I guess) -- but then there's building around sacrifice and enters-the-battlefield effects. There's the possible impact on deckbuilding -- depending on where undying falls on the mana curve, it benefits certain strategies. Cheap undying creatures lend strength to mid-range decks; the small guys trade effectively and turn into hefty attackers, buying you time to get your expensive and powerful control or burn options online; expensive undying creatures support heavy control decks, where the finishers of choice have built-in redundancy. There's also the subtle effect of making +1/+1 counters occasional liabilities, which is intriguing. Good keywords are exciting and suggest powerful plays while providing strategic depth; passable keywords give some zim to otherwise boring creatures. Islandhome as it exists doesn't do any of that.

So,  what would I have Islandhome do? First, it wouldn't be a keyword. It'd simply be a linked set of abilities that appear together and provide a meaningful discount on the mana cost. Second, the abilities by themselves would be strict drawbacks -- that is, they'd be downsides with no tricksy upside. Third, they'd play into blue's land-changing mechanics. Finally, all creatures with islandhome would have double blue in the casting cost.

Islandhome -- This creature can't attack unless the defending player controls an Island.