karros turns into an unraveller chtonic demon. its a different type from ryloks. they are more tentaclier than ryloks and can summon more mini tentacles to harass players.
the ryloks are the humanoid chthonic creatures with tentacle beards, back limbs and sometimes wings. they ripped the backlimbs (spines?) from weaker ryloks to wear it as trophies and for prestige between them. oppressors are one of the higher tier rylok class monster. so its not wrong that they drop rylok mark. theres a zantai’s Ashes of Malmouth misadventures around here somewhere that tells us more about them ryloks.
edit: found the link to the rylok misadventure: