The tribes of Ixalan are one of the biggest themes of this block that we have yet to see pay off in a big way. That said, with exciting new tribes like Pirates and Dinosaurs alongside fan favorites like Merfolk, it's only a matter of time before someone finds the perfect mix of tribal synergies to put up a great performance. If Merfolk is your tribe of choice, Akerlund has put together a great starting point:

U/G Merfolk -- Rivals of Ixalan Standard | Akerlund, 5-0 Standard League

• Creatures (32)
• 1 Tempest Caller
• 3 Jade Bearer
• 4 Deeproot Elite
• 4 Jungleborn Pioneer
• 4 Kumena, Tyrant of Orazca
• 4 Kumena's Speaker
• 4 Merfolk Branchwalker
• 4 Merfolk Mistbinder
• 4 Silvergill Adept

• Instants (4)
• 4 Unsummon

• Enchantments (2)
• 2 Deeproot Waters

• Lands (22)
• 5 Forest
• 5 Island
• 4 Botanical Sanctum
• 4 Hashep Oasis
• 4 Unclaimed Territory

• Sideboard (15)
• 1 Tempest Caller
• 2 Deathgorge Scavenger
• 2 Essence Scatter
• 3 Naturalize
• 2 Negate
• 2 Seafloor Oracle
• 3 Spell Pierce

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Deeproot Waters and Jungleborn Pioneer team up with Kumena, Tyrant of Orazca to ensure that you're able to go much bigger than opposing creatures decks, given enough time. The ability to consistently generate Merfolk tokens so that you can activate more and more of Kumena's abilities turn after turn quickly lets you turn board stalls into an overwhelming advantage. And that's to say nothing of Kumena teaming up with sideboard copies of Seafloor Oracle to help you chip away at opposing life totals while pulling ahead on cards.

If you're looking to get aggressive with a Merfolk beatdown deck in Standard, this seems like a fantastic place to start. You're a little light on actual removal, but Unsummon will frequently give you the opening you need. If you're more worried about control decks and sweepers, then maybe Spell Pierce is a better fit than Unsummon. No matter what kind of field you're expecting to face, there are enough powerful Merfolk and efficient Blue interaction that you should be able to stay competitive against most anything in Standard.