What are the Mariners in Elden Ring? Answered

gamepur.com:

Chances are at one point or another in Elden Ring players will stumble into a Tibia Mariner. While not the most pressing threat at first, this boss appears in multiple locations on the map to ruin perfectly good shallow water areas. What makes them so special? They are actually tied to a special vendor in the Lands Between.

Tibia Mariners are skeletal bosses with a purple hue that paddle through shallow water in a small rowboat. The first one encountered in the game is usually the one near the Summonwater Village Outskirts. This boss doesn’t provide much of a challenge, and will reward the player with an interesting summon upon defeat that is actually quite useful. The Skeletal Militiaman Ashes summons two skeletons that can revive from the dead if they are defeated in combat and not struck again before they can get up.

The main reason Tarnished seek out these Mariner bosses, however, is that they reward Deathroot upon being defeated. Deathroot is a special item that peaks the interest of the Gurranq Beast Clergyman, a vendor that provides unique items based on the amount of Deathroots fed to him. He is located at the Bestial Sanctum, which can be accessed by finding a waygate in Limgrave north of the Third Church of Marika.

There are several Tibia Mariners to fight throughout the map. The other three locations are as follows:

While the mariner in Summonwater is a pushover, these bosses get deadlier as they are discovered further in the map. They eventually summon a lot of adds and can even cause a giant skeleton to rise up under the player to delete them if they aren’t careful.