In this update, they added 5 bosses, in order The Flaming Orchid, The Moonlight Aster, The Winter Bloom, Kusuma and Timira the Many-Headed.
The Flaming Orchid, The Moonlight Aster, The Winter Bloom as far as i killed them they dont drop anything super value, I suspect that the loot is similar to regular asuras, without any rare drops, or at least so far no such information appears. So far best loot for me was crystaline armor and oriental shoe.
Kusuma, similar to mentioned above "asura minibosses" doesn't seem to have any rare drop, more of a standard mid-value item set
Timira the Many-Headed she is "main" boss of marapur and she can drop all "naga" items, additionally, reward boxes for completing the first two stages of combat (scooping water and "sacrificing health") can also give us these items. On live server i didnt get any of them so far but on test server i drop naga axe from her.