The Lost Explorers are the second or fourth boss of The Venomous Abyss raid, depending on your route.
This is a three-target fight where players are trying to prevent Mor'zahi from completing his Final Ascension. To prevent this, players feed Disgusting Fish to one of the possessed tortollans before Mor'zahi's cast finishes. Each tortollan can only be fed once, and players need to defeat the possessed tortollans before they run out of fish.
Three bosses. Two need to be tanked. Do NOT let them stack.
There is also Mor'zahi and Trader Gebbo. Gebbo tosses out fish - someone needs to pick up the fish and hit one of the turtles with it before Mor'zahi gets to 100 energy. You can only hit each turtle once.
A turtle hit with a fish gains an "ultimate ability". They are:
Nama: Three large soaks, each needing several players to soak.
Iku: Fire and frost circles on random players. These leave patches on the floor - when they do, run into the opposite type to clear the debuff.
Gebbo: Throws down mushrooms and a bomb. When the bomb explodes it produces a ring of fire - bounce on a mushroom to avoid this ring.