I would also add that Davos has the most Merling related content of any POV characted save maybe Brienne and Iron Islanders like Aeron. He sails to the Three Sisters, speaks with the Borrells about their 5000 year old fishy-person mark, goes to the Merling Court of the Manderlys (also definitely merling hybrids, anytime you see fat cannibals be on the lookout). The Manderlys even drop hints to Davos about Frey Pie and their cannibalism.

Brienne is the one who speaks with Nimble Dick and gets the lore dump on Merlings, as well as the one who fights Biter and gets her face eaten by him. Read that fight with Biter, it’s very obvious she’s not fighting with a human being. She’s jamming her armored gauntlet into his eyes and punching his face like 10 times and it does nothing to him whatsoever but is described as hitting a big wet ball of dough. Brienne of Tarth shoving her armored gauntlets into your eyes should do something to most normal people. Merlings and their hybrids seem to be exceptionally strong, have extreme pain tolerance and are very difficult to kill (See the Manderly guy getting his belly cut open and continuing to fight and not dying) and often have sharp teeth. The Hybrids on the Thousand Islands file the teeth of the women they offer as sacrifice, so it seems like the sharp teeth only exist in 100% merlings and not weaker hybrid strains like the Manderlys