INTERACTIONS:

    copying an activated mutavault with a vialed Phantasmal Image to ramp yourself (just did this for like the second time ever the other day)

    tapping an opponent creature with a merrow reejerey trigger when you cast harbinger of the tides, then bouncing it with the harbinger's trigger

    returning Oboro, Palace in the Clouds to your hand in response to Liliana's +1 to discard it

    with just oboro and mutavaults in play, if you need UU and haven't played your land for the turn, you can float blue with oboro, return it to your hand with mutavault's mana, then replay it to tap for a second U

    with kira, great glass-spinner on board against ad naus, when they cast lightning storm for the win, you can pitch a land from your hand to target one of your creatures, which is countered by kira's ability, which counters the whole lightning storm

    the fact that master of the pearl trident only gives your merfolk +1/+1 and islandwalk, but lord of atlantis gives ALL other merfolk +1/+1 and islandwalk, which is relevant mostly in the mirror, but also notably for opponent mutavaults in 8-rack or slivers.

    phantasmal image can copy hexproof and pro-blue creatures, because its cloning ability does not target and doesn't use the stack. most notably used to copy affinity's etched champion to block it.



SIDEBOARDING:

Sideboard out Aether Vial against most grindy Black decks with a lot of discard and removal. The tempo which Vial generates is not enough value so the card isn't worth it.

    Vapor Snag is good against Black decks because you can bounce your own creatures to save it, making it quite a flexible card. What Vial does is that it puts a bunch of creatures into play quickly, but that effect isn't something you want if your opponent is killing and discarding your most important cards. However, Vapor Snag can protect your important threats, and allows you to set up the big turns and even helps you deal a lot of damage all of a sudden.

    Another general rule is to side out an Island or two against the control decks with Path to Exile. In those matchups, you just want to either color screw them with Tectonic Edge and Spreading Seas, or to outvalue them. In those games, Path to Exile becomes a really bad card for them if the land you can get is actually important to you. Also, the games go longer and you're not trying to aggro them out quickly, so it is fine if you operate on fewer lands at the beginning of the game.

    Board out Spreading Seas against super aggressive decks, especially on the draw. You cannot afford to spend two mana on an effect that doesn't affect the board.

    Cut the expensive cards like Master of Waves against the combo decks. They are not killing your creatures, so you don't need a big card for recovery. Often, you cannot even tap out for it, because you need to hold up mana for counterspells.