The main thing is, its method of attack is too unique; it attacks by moving in a circle.
Its speed isn't particularly fast, taking about three seconds to complete one circle, but the problem is that it consists of five blood phantom arms each holding a scimitar, so one circle equates to five slashes.
Three seconds, five slashes; this is already a terrifying rate of attack. A Legendary Warrior can only make five slashes in six seconds. Don't think it's slow; each slash here refers to a full top-down chopping motion, not the small scope chopping, which might be fast but lacks enough power to pose a significant threat.
Such attacks, if carried out among densely packed unarmored or lightly armored creatures or crowds, turn into a slaughtering whirlwind. Wherever it rolls, blood sprays, limbs sever, and bodies pile up; flesh and blood cannot withstand the madness of this cutting.
