I have new forms for legendaries, captains, and espada.

Shingami:
Zanpaktou Fusion
Fuses with his/her zanpaktou spirit.
Captains only, need 300 posts. Lasts ten posts.

Vizards:
Hollowfication
A controlled hollowfication, takes on features from his/her inner hollow.
Legendary Vizards only, 300 posts, lasts 10 posts.

Arrancars:
True Form
2x the power of a resurreccion, becomes more like their hollow form.
Espada only, 305 posts, lasts 10 posts.

Bounts:
Ultimate Doll
The doll grows 2 times more powerful, doubles in size, and is more menacing.
Legendary Bount only, 300 posts, lasts 10 posts.

Quincy:
Maximum Power
Has the effects of removing a sanrei glove, only you keep your powers.
Legendary Quincy only, 300 posts, lasts 10 posts.

A couple things. . .Zanpacuto fusion is a permanent affair. I think your thinking of kyuuokakkai or however you spell that. It's the ultimate attack/Form of a zanpacuto. Fusion makes you and your zanpakuto one. Forever.

Hollowfictation is the process of become a vizard, Not becoming a stronger one. However, Vizard can take on a sort of "Hollow form" so the principle is sound.

That's all. Just felt like throwing in my two cents.