Yuval

Member of the red-eye tribe. Reputed to be a merdude, but when the party met him he was made of stone. Cause of aggressive merrows in the taak. Wielder of water tendrils. Possible maker of the weird spire islands. Driven off from Guara in the infamous cart battle with ally/boss Durnen and an elven archer.

Description
Of all the Red Eyes, we probably know the least about what this dude looks like. Not because we haven't see him, but because it seems like he has the power to shift forms or in some way alter himself. He (even making a guess here on gender) presented to the Lake Norka taak as a merman, but the party later encountered him wearing stone skin in Guara.

Background
Very little is known. At some point he came to the taak and began attacking boats crossing a certain distance into Lake Norka. Whether his motives in doing this were to incite conflict betwen the merfolk and the land-dwellers or to get both sides to stay away from whatever he was doing (perhaps related to the mysterious spires on surrounding islands) is unknown.

"Let Your Waves Crash Down on Me" (1x7)
The party ran into some of Yuval's handiwork, vicious water tendrils, as they were exploring Lake Norka. Their boat, the Wind's Pride, was ultimately a casualty.

"And No Rivers and No Lakes Can Put the Fire Out" (1x10)
Zen said that a strange visitor by the name of Yuval had been by many moons ago. He had the ability to control water, looked like one of the merfolk, and had red eyes. A while after his visit the strange lights had appeared in the nest's holes, but it seemed uncertain whether these were directly connected. M'Shel confirmed this, saying that tensions between the various lake communities were present even before Yuval had come along.

"Nothing Can Fly With This Broken Wing" (1x11)
The party first encountered Yuval (see also "Stone Dude") at the Battle of Guara, fighting alongside Savas and Durnen as well as a host of other monster allies. This time he was landborne and covered in stone. After defeat at Guara, he dragged Durnen's body away into the forests while Felegum and Zeno gave chase, but he was too fast for 'em. Before dashing off, Yuval did indeed demonstrate his stone spire skills, possibly connecting him to the strange islands in the lake, both around the party and on the cart.

Durnen
They are definitely working together (both Red Eyes) but the how and why of it is unclear. Ultimate power? Possibly.