Listen, I know we already have an "undead" tier 3 boss. Well... he's not really undead but people just say he is. But at about 5am in the morning, without having any sleep, I got this new idea. A phantom boss. Like... a super phantom!
He'd be a bit faster and a lot stronger than the other phantoms. He should also weild a Gran Faust. The actual one. Except he should have the ability to swing that sword like a Leviathan (3 slashes) and his charge attack should be 3 phantasmal launching swords (like the Divine Avenger's) but with a bigger size (as big as the Gran Faust's single phantasmal sword charge). Keep him the same size as we are, I find it more difficult and fun.
Phase 1: He'll be spamming his charge attack from the very top of his room, and the launching swords can reach the very end of the room. Only option is to gun him or get close and shield a lot.
Phase 2: He will start moving and attacking the players with his Gran Faust in a similar way that normal phantoms do, but instead he cannot be knocked back or knocked down. During this phase he will absorb gun shots so you HAVE to deal damage to him with a bomb or shield.
Phase 3: He'll go back to doing his sword spam at the top of the room. A vase (like the fire and oil ones) will appear in the middle of the room, it'll respawn over and over after its previous use. 2 regular phantoms will pop out and go for the you. Once you defeat them you have to throw the vase at the glowing "orb" state they'll be in, then they'll be "sealed" and gone forever. The super phantom will stop doing his sword spam after the phantoms are defeated and he'll attack you like he did in the last phase. Except he'll be faster, less forgiving, stronger, and he'll dodge more often. Guns will also be useless during this phase. Once he's defeated and goes into his orb state you have to throw the vase at him and seal him. Do this fast, if not then you'll repeat the phase.
That's basically it! Too lazy to describe his palace or anything though. Should be similar, but more creepy, than the graveyards. Somebody else describe that. Also, with his tokens you should be able to get the same weapon that the phantom's hold. Maybe you should call it the "Knightmare Striker" :D. It'll be another 5 star weapon that inflicts shadow damage. And it'll have the same charge too. 40 tokens sounds like a good price. Yup yup!
You just described a T3 Phantom.