Mantis Petra

Behaviour and Tactics
They hover just outside of The Knight's melee reach. They fling scythes at the player that will swoop down in a parabolic arc, slow at the apex, then come back up.

If possible, try to get slightly above them to lure them close and hit them with a Nail Art or Spell before they hover away again. Alternatively, using Howling Wraiths/Abyss Shriek or Grubberfly's Elegy will close the distance.

They often show up in groups with another Petra or a Mantis Traitor. Get rid of them first, as their aerial attacks make fighting ground-based enemies aggravating.

Location
Also found within the Colosseum of Fools. (Strangely enough only the Mantis Petra marked by a red circle will respawn when reentering the room, all others will only respawn when the player rests at a bench)