|This article or section needs to be cleaned up to a higher standard of quality.
Druids possess the unique ability to shapeshift, which means turn themselves into something else. They can become a bear, a panther (night elves), a lion (tauren), a cheetah, a sea lion, both slow and fast birds, and, with the right talent templates, a Moonkin or a Tree of Life.
The shapeshift bar is a UI element that is available for several classes. As mentioned above, druids have a shapeshift bar which can contain Bear, Aquatic, Cat, Travel, Dire Bear, Moonkin and Tree of Life forms. Warrior stances are placed on the shapeshift bar, as well as rogues' Stealth ability and shadow priests' Shadowform, as well as Paladins Auras.
There are other abilities that seem like they could be placed in the shapeshift bar, but Blizzard has not decided to do so. These are hunters' aspects and shamans' Ghost Wolf ability. One potential reason for this is that these abilities are not requirements for other abilities (for example, a druid can only Swipe while in Bear or Dire Bear form; hunters are less effective at ranged DPS with Aspect of the Monkey, but they can still use any of their abilities). Although hunter's don't have that bar there a various addons that are available to download to make one.
As of Patch 2.3, trying to use an ability that may only be used in caster form, will make you leave the form and use that ability. This means that you can shift from one form to another in one action. If you don’t have mana to shift form, you will get an error message and remain in your current form. This can be disabled with: /console autoUnshift 0