Barbatos?

https://grandorder.gamepress.gg/solomon-preparation

His/it/whatever class is assassin.

There are seven demon pillars, each being a different class and having a raid of its own. Barbatos is the assassin pillar, so DPS casters (Illya and Xuanzang are the only SSR ones) are recommended for its raid. Barbatos's raid in particular drops valuable ascension materials that have not been in recent event shops (pages and gears), which is why most people will be farming it first.

if you want to get a shot at barbatos you better be in USA or put up your alarm clock to farm some. thanks to time zone difference I bet the damn thing will be dead by the time I wake up...

it definitely isnt an assassin class boss enemy who drops demon hearts... nope totally doesnt drop them, you shouldn't bother with farming this one.