This is one area where an RPer can take some liberties with their creativity, though it is still too easy to cross the line that separates good ideas from over-the-top. This post is going to go over the Arrancar Zanpakutoh in sealed and unsealed form.
An arrancar's resurreccion is simply the sealing of one's hollow powers into the form of a weapon. The style is completely one of their choosing, allowing them a much broader range of zanpakutoh forms than a Shinigami's or Vizards' sealed zanpakutoh. More than likely, this is the reason why an Arrancar has no fear of taking a backward step in their evolution. Their true form is sealed to maintain their human form and to conserve energy during down-time.
Because their powers are being sealed, a physical change is noticeable. A change in capabilities is also seen. Their speed, strength, stamina, durability, and spiritual power are all augmented and they have access to the full capabilities of the abilities they have shown up to that point and also access to completely new abilities. These new abilities tend to reflect their true form. Aguila was able to use steel feathers to crush opponents. Findor Carias has his pincers and was able to shoot powerful wisps of water that could harm opponents.
When the Arrancar releases their zanpakutoh, they usually lose the individual weapon to adopt natural ones on their body, such as Findor's pincers, Poww's fists, Grimmjow's body in general, Luppi's tentacles, etc. Out of the thirty-some-odd Arrancar whose resurreccion we have seen, only nine or ten Arrancar retained actual weapons that were not parts of their bodies, suggesting that while not rare, it certainly is uncommon.
It is possible for an Arrancar to seal a second form, but Ulquiorra is the only individual to have done so in both Manga and Anime, and so this suggests that it is a very rare ability for one to learn, let alone achieve.
by 
Subject: Arrancar Zanpaktou 
