Ultimate is the resource needed to cast Ultimate Abilities. There are a total of 32 Ultimate Abilities available, but you may only choose from up to 16: one each from the 3 skill lines in your class, 6 from the Weapon Skills (which require you to use that specific weapon type), and 8 available to all classes, two of which are mutually exclusive, since you cannot be both a Vampire and a Werewolf at the same time. There is at most one Ultimate Ability per skill tree. Only one Ultimate Ability may be slotted on each bar at a time, so two different Ultimate Abilities can be slotted in total. Ultimate regeneration triggers upon hitting a non-trivial enemy with Light or Heavy attacks, when healing others (healing yourself does not count), or upon blocking an attack. The hidden Ultimate regeneration buff lasts for 9 seconds, generating 3 ultimate per second, for 27 total.
The maximum Ultimate that you can accumulate is 500. Casting your Ultimate Ability consumes all accumulated Ultimate regardless of what the listed Ultimate cost of the ability is.
Some skills or items may cause you to gain additional Ultimate, allowing you to use your Ultimate Abilities more often. Others may reduce costs instead. The Aetherial Well furnishing allows for instant restoration of Ultimate from within a player house.