The blue member of the Llanowar Elves cycle. What's mana-acceraty, but feels blue?

Not sure if this is too versatile, it could easily just be "lands you control".

I don't think it's too bad - you'd sacrifice your own mana acceleration in exchange for slowing your opponent down a bit (and, eventually, punching them in the face with a Sea Serpent.) I don't see that as being overpowered. Though maybe it shouldn't fly, despite the homage to Birds of Paradise you'd have to relinquish.

Hm. Maybe it should be 0/2 and ": Untap target Island. : Target land becomes an island until end of turn."

I would like to point out that Wizards hasn't had a cheap permanent that can change it's opponent's land at instant speed since Apocalypse. I know I've read comments from their website that bemoan this mechanic for being too good at screwing up people's turns... the big beef being that cards like Sea's Claim, for example, only ever targets one land. A card like this can start by stalling early plays, color screwing the correct color in mid-game, then stopping powerful man-lands from working in the late game. All that, and it requires a lot of thinking about which lands to use it on when... a very important decision that gets very trivial sometimes.

Whether you think it's fair is another story. Apocalypse was a long time ago, and it might be okay nowadays. I don't know. It sure does seem like a lot of people want this ability to exist. Every time I see someone suggest it, it is immediately followed by "You know, this seems fair. How come we haven't seen any good 'Thing Xs'".

People keep claiming that. But Lorwyn had Streambed Aquitects. It is notable that Grixis Illusionist and Tideshaper Mystic both managed to dodge the Reef Shaman mana-denial problem, though.

On reflection, my best guess is that:

• There probably is room for cheap U mana denial
• But it shouldn't be the default, so the simplest way for this card to feel U/G is probably to say "you control".