Merfolk
A Modern deck, by Paeng_Paeng
1st place at a tournament in Magic Online on 2020-06-30

Maindeck:

Artifacts
4 Aether Vial

Creatures
4 Benthic Biomancer
4 Harbinger of the Tides
4 Lord of Atlantis (Not currently legal in Modern)
4 Master of the Pearl Trident
4 Merfolk Trickster
4 Merrow Reejerey
4 Silvergill Adept

Enchantments
4 Spreading Seas

Instants
3 Dismember
2 Spell Pierce

Basic Lands
12 Island

Lands
1 Castle Vantress
4 Mutavault

Legendary Lands
1 Minamo, School at Water's Edge
1 Oboro, Palace in the Clouds

Sideboard:
3 Damping Matrix
2 Damping Sphere
1 Grafdigger's Cage
1 Relic of Progenitus
2 Tidebinder Mage
1 Aether Gust
2 Deprive
1 Kira, Great Glass-Spinner
2 Ashiok, Dream Render