He is the first boss to be made playable, he can't shoot, or parry. However he starts with a much larger hp and stm pool.
He has a basic 3 hit combo with a much stronger dmg output.
His heavy attack is where the difference comes in, upon pressing the heavy attack key, he summons a clone who will stay in place and direction and deliver a full 3 hit combo.
Next to be completed is Second Knight - Gray.
Other bosses will each have their very own little gimmick. The first knight will use magic, and indeed will be able to use the reaper :)
Expect the update in 2-3 days.