I have one idea, you should make a boss with this kind of stats (i'm not an artist so i won't make a picture)
Doom Blade
HP:25605
Strength:80
Defense:125
Speed:100
SP ATK:165
SP DEF:140
Weakness:Light,Poision,Holy
Resistance:Twilight (light & dark, not the stupid series)
Immune:anything else
Drops:nothing
Rare Drops:his blades
You can change the stats because i haven't played your game and they might be too low or too high or whatever.
He would be a floating black coat like thing with two blades floating above him that are purple and are beam-ish, not like lightsabers though.
Modification: Dangit they aren't part of that form, i guess........... eh i dunno