[Modern] Merfolk (Sideboard Help!)

Hello all! I've been contemplating getting into Modern for a while now (Standard just seems to becoming worse and worse of an investment) and I've decided to ever so slowly began a Merfolk build.

http://tappedout.net/mtg-decks/12-05-14 … merfolk-2/

Land (20):
13x Island
4x Mutavault
3x Cavern of Souls
Creatures (28):
4x Cursecatchers
4x Lord of Atlantis
4x Master of the Pearl Trident
4x Phantasmal Image
4x Silvergill Adept
1x Sygg, River Cutthroat
4x Merrow Reejery
2x Kira, Great Glass-Spinner
1x Master of Waves
Artifacts (4):
4x Aether Vial
Instant (4):
4x Vapor Snag
Enchantment (4):
4x Spreading Seas

Sideboard:
Creature (4):
2x Tidebinder Mage
2x Spellskite
Artifact (3):
1x Relic of Progenitus
2x Grafdigger's Cage
Instant (8):
1x Swan Song
2x Steel Sabotage
2x Hurkyl's Recall
2x Squelch
1x Dismember

I certainly won't call the mainboard too original in any way, at all. It seems pretty much all Merfolk decks only differ by a few cards.

Mostly what I'm worried about is the sideboard. I have not played Modern before and therefor I'm not quite sure what I should have and for what reason. I think I've done a pretty decent job for general matchups but I'm note quite sure.

I would certainly appreciate any and all feedback. Thanks!