Vile Knight is enemy that are unique to Sunken Palace. Another enemy that can be also found in Sunken Palace is Great Imp. It is suggested that there is skeleton underneath the armor.
Strategy[]
They possesses weapon that can be thrown like a boomerang that would fly and then return back to them. The sword can be reflected back.
Weakness[]
If you are good with Precision Strike then you can use their own weapon against them.