Shapeshift into cat form, increasing melee attack power by (Your Level * 2) plus Agility. Also protects the caster from Polymorph effects and allows the use of various cat abilities.
The act of shapeshifting frees the caster of Polymorph and Movement Impairing effects.
Cat Form is similar to a Rogue in that it relies on an Energy bar and combo points to use most of its skills. Druids in Cat Form also gain the ability to Track Humanoids, making a cloaked Cat Form Druid perfect for PvP ambushes. - Most players choose to be a feral druid so that they can re-spec to any other roll whenever they please. But one of disadvantages of being one is that their damage potential, dodge, and other important factors cannot challenge that of a rogue, and rogues have much more tactical abilities.
Attack Power is increased by the formula: (Strength x 2) + Agility + (Character Level x 2) - 20
Feral attack power is increased by the formula: (Weapon dps - 54.8) * 14
Aside from the contribution from Agility, Strength and straight attack power on a weapon, cat form benefits from additional Feral attack power mentioned above. Example: A weapon with 281.5 dps, such as heroic [Lupine Longstaff], would grant an additional 3173 attack power.
Procs from "Chance on Hit" enchantments on weapons, since Patch 3.0, now work while in Cat Form. This includes weapon enchantments, such as Mongoose, and temporary weapon enhancements, such as Windfury Totem.
Generates energy via 2 ways only: 20 energy every 2 seconds or the talent Furor.
Cat Form uses Energy instead of Mana and can [Stealth], like a Rogue.
Cat Form has an innate threat reduction component. This is currently believed to be at 29% reduction, which mirrors the threat reduction of Rogues. (see Threat per Class)
Blizzard has redesigned the Cat and Bear forms, which were released with Patch 3.2.0. There are now 5 different fur colors, designated by your hair colour (Night elf) or fur colour (Tauren).
Talent improvement
Talents that affect specific abilities are not listed here, in order to keep this list shorter.
A druid in Cat Form can use both stealth and Track Humanoids to ambush people in PvP. By default, if you have no profession tracking on, when you shift into Cat Form, Track Humanoids is automatically activated once you have learned it.
Note: If you're tracking repair or other helpful NPCs or mailboxes, Track Humanoids will override this. When you shift out of Cat Form again, the icon of Track Humanoids will remain due to a display bug, but actually you're tracking nothing then, until you select something or shift into Cat Form again.
Cat Form also has an arsenal of difficult-to-remove physical DoTs (like a Warrior's [Rend]) which can be used to tear casters apart in PvP.
Patch changes
Patch 3.2.0 (2009-08-04): Mana energizes that occur while in this form will now appear in the combat log and floating combat text.