When Merfolk Surveyor enters the battlfield, explore-clash. If you win the explore-clash, gain 3 life. (To explore-clash, you and an opponent each reveal the top card of your respective libraries. Put any lands revealed this way into their owner's hands. Put a +1/+1 counter on this creature for each nonland card revealed this way. Then, each player who didn't get a nonland puts the card back or into their graveyard. You win the explore-clash if the mana value of your revealed card was higher.)
When Merfolk Tunnel-Guide enters, you get a three-time boon with "Whenever one or more Merfolk enter under your control, target Merfolk creature you control explores."
Flying When Merfolk Wayfinder enters, reveal the top three cards of your library. Put all Island cards revealed this way into your hand and the rest on the bottom of your library in any order.
Flying Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.
"The merfolk of the Pearl Trident have risen from the waves since the earliest days, at times allies to humans, other times enemies. Now their power is cresting again, and who can say which way the new tide will flow." —Kalis, Onean scholar
Tap an untapped nontoken artifact you control: Add {G}. Tap two untapped nontoken artifacts you control: Exile the top card of your library. You may play it this turn.
"Why fear artifice? Is it not also of this world?"
Merieke Ri Berit doesn't untap during your untap step. {T}: Gain control of target creature for as long as you control Merieke Ri Berit. When Merieke Ri Berit leaves the battlefield or becomes untapped, destroy that creature. It can't be regenerated.