Curious, thoughtful, and analytical, the Zendikar merfolk are natural explorers. Although the merfolk are born in the water, their appearance is more human than fish. They have muted skin colors, including ivory, beige, silver, and pale gold. They have residual fins on the backs of their arms and calves. The fins are sometimes streaked with brighter colors, such as green and blue. They have human-like hair in shades of silver, gold, and light browns. But like their fins, the merfolk's hair often has streaks of bright color as well.

Although merfolk are a common sight in the settlements and trading posts of Zendikar, they are a race in decline. Merfolk tend to be more solitary than other races and don't cultivate large communities. But even merfolk who spend most of their time exploring will establish a home base, a place they return to before setting out again.

The merfolk believe that the world is divided into three realms: Emeria, or the Wind Realm, which was once ruled by the goddess Emeria and includes the sky, the wind, and the clouds; Ula's Realm, the underwater realm; and Cosi's Realm, which comprises everything else.

The merfolk recognize these divinities as the forces that drive the world, usually adopting the creed of one of the three as their own. Emeria, also the name used to refer to the ruined floating castle in Tazeem believed to be where the goddess once dwelt, brings an ethereal wisdom to her devotees. While merfolk are not native to Emeria's sky realm, they connect with her airy mysticism, many of them following her creed and striving to learn ways to restore her to rule in her floating castle once again.

Followers of Ula, the water-realm deity, pride themselves on being blunt and straightforward in their dealings with others. Ula-creed merfolk operate the famed research facility at the Lighthouse at Sea Gate and make excellent navigators and ruin scholars.

Ula is a "pure" merfolk who dwells at the bottom of Halimar. He is the true ruler of water realm: the seas, the oceans, rivers and lakes. The same upheaval that destroyed Em's castle also robbed Ula of his memory, but it left him with the knowledge of the task he must complete, the wrong he must avenge. He swims endlessly through the Halimar trying to rediscover what he was meant to do. Ula's Guardians are two massive leviathans who protect Ula as he swims aimlessly through the dark water. —Chronicles of Ula

Zendikar is so dangerous and inhospitable that all other terrain is considered to be under the rule of Cosi, the Trickster. Cosi is believed to take the form of handsome humanlike being with a mischievous grin. He carries two kor-inspired hooked ropes that he uses to meddle in mortal affairs. Cosi has a chaotic nature. He will lure, scheme, and deceive for no reason but to incite chaos. Misfortune is usually blamed on Cosi's meddling.

Almost no one admits to being an adherent of Cosi, the trickster. Blamed for the misfortunes of the world, Cosi is seen as a force of chaos—and yet the merfolk believe in his dynamic, incredible power. If someone could channel the untapped forces ruled by Cosi, they say, that individual would be one to fear, indeed.

Merfolk armor is streamlined, as intricate as coral, and revealing, as they need good mobility in the water (good thing they have toned swimmer's bodies!). Their clothing and metal rings serve more than a decorative purpose; they can be used to bind up the loose fins on their forearms and calves when out of water. Merfolk wizards and non-wizards alike tend to favor staves, spears, and javelins, preferring weaponry that can hit the mark both underwater and above. Some merfolk master travelers accumulate a veritable reef of accreted artifacts, gems, and other magical discoveries, and almost every merfolk is a storehouse of information. Their dedication to the art of writing is unmatched among the races of Zendikar; their written language is highly developed pictorial system, thickly layered with meaning, so scrolls of tanned hide are commonly found on their person.

Cosi's Trickster, Merfolk Wayfinder, Sejiri Merfolk