These are another melee fire spectres with a bunch of combo attacks similar to Karui Backburners. They use Cleave with good damage multipliers baked into skill, an Axe combo skill and a gap closing Dash slam, all skills have 50% to 75% phys to fire conversion, and their skills also spawn homing balls which deal very little damage and not worth scaling.

0:00 Eater of Worlds

1:01 The Black Knight

2:26 Maven

6:05 Uber Elder

9:30 Map Clearing

I think Karui Backburners are just better with the same gear, gems and everything.

My PoB https://pobb.in/AKkIXixIGJYL

https://poedb.tw/us/Karui_Firespeaker#KaruiFirespeakerLegionKaruiSergeantMeleeFireStandalone

The easiest way to get them is to buy karui emblem from Faustus and one other emblem of your choice and run 2 way domain of Timeless conflict. It spawns as rare mob, look for a big axe guy.