U/G Merfolk
A Modern deck, by Jeremy Bertarioni
4th place at a tournament in Cincinnati, Ohio, United States on 2017-10-21

Maindeck:

Artifacts
4 Aether Vial

Creatures
4 Harbinger of the Tides
4 Kumena's Speaker
4 Lord of Atlantis (Not currently legal in Modern)
4 Master of the Pearl Trident
1 Master of Waves
4 Merfolk Branchwalker
4 Merrow Reejerey
4 Silvergill Adept

Enchantments
4 Spreading Seas

Instants
2 Dismember

Legendary Creatures
1 Kira, Great Glass-Spinner
1 Kopala, Warden of Waves

Basic Lands
4 Island

Lands
4 Botanical Sanctum
2 Breeding Pool
4 Cavern of Souls
4 Mutavault
1 Unclaimed Territory

Sideboard:
2 Grafdigger's Cage
3 Relic of Progenitus
2 Deeproot Waters
3 Ceremonious Rejection
1 Dismember
2 Dispel
2 Spell Pierce