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A player cannot be a vampire and a werewolf (or infected with the diseases that cause each transformation) at the same time; werewolf skills are most useful to stamina-based characters and vampire skills are most useful to magicka-based characters. If you wish to clear your infection, a Priest of Arkay in the Mages Guild within Rawl'kha, Evermore, or Riften can assist you.
To become infected, one can be bitten by another player, be attacked and infected by a NPC in the game (rare occurance), or, as a last resort, buy the item in the crown store. One can become infected with vampirism only during the New Moon phase, which occurs every 8 days or with Sanguines Lupinus (leads to werewolf) during the Full Moon phase. To check the current moon phase, look at the water level in Riften where the dock steps enter the water. During the proper moon phase, and only within The Rift, Bangkorai, or Reaper's March at certain spawn locations one can become infected from a bloodfiend (vampire) or werewolf -- but only if they are attacked before these NPCs are killed as it appears they do not respawn.
Developer Comments – Werewolf Changes: There were a significant number of changes made to Werewolf this update. Some of these changes were made to improve the quality of life with leveling and maintaining the form, while others open up new gameplay possibilities.
First, you’ll find leveling and maintaining your Werewolf is now considerably easier. The Devour passive is now granted automatically from the very start, so you can sustain the form better at lower levels before you’ve unlocked all the other skills. We’ve also significantly reduced the experience requirements to morph all skills.
Second, you’ll be able to do more core combat actions as a Werewolf, such as resurrecting your allies or using Synergies. Werewolves will have a much easier time engaging in group content now that they can help their friends more effectively. This, coupled with some other changes such as the Blood Rage passive triggering on damage dealt instead of damage taken, means they can be more viable in group PvE activities such as dungeons.
Finally, many morphs and abilities were changed to improve the cohesiveness of the Werewolf kit. Some combos and effects that weren’t very effective have been removed, while others were tweaked to better support the fast and ferocious playstyle of the Werewolf. As an example, we removed the stuns from Pounce and Piercing Howl, but dramatically improved Roar by making it instant cast, fear more targets, and have more competitive morph effects.
Developer Comments: These bonuses were moved to passive abilities to help reinforce the feeling of progression you get from leveling the Werewolf skill line. It also allows for extra space to add more information to the Werewolf Transformation tooltip about all the other bonuses you have while transformed, such as your Max Stamina being increased or your Heavy Attacks dealing splash damage.
Blood Rage: This ability now increases the timer of your Werewolf Transformation when you deal damage, rather than when you take damage. It adds 2/4 seconds to your timer with a 5 second cooldown.
Hircine’s Bounty: This ability and its morphs now heal based on your Max Health; Hircine’s Bounty and Hircine’s Rage heal for 45% of your Max Health, while Hircine’s Fortitude heal for 60% of your Max Health.
Infectious Claws: Updated the visual effects for this ability and its morphs.
Pounce: This ability and its morphs no longer stun the target if they were already set Off Balance.
Pursuit: This ability now also increases your Movement Speed by 15/30%.
Savage Strength: This ability now also increases your Spell and Physical Resistance by 5000/10000.
All Werewolf abilities now require less experience to morph. The experience requirements to level up the Werewolf abilities now match the Weapon Skill Line abilities, and the Werewolf Transformation Ultimate experience requirement now matches Class Ultimate abilities.
Curing Lycanthropy will now refund all Skill Points that are invested in the Skill Line.
Fixed an issue where casting another ability while in the middle of a Werewolf Heavy Attack would cancel the Heavy Attack, instead of queuing the ability to cast when the Heavy Attack completed.
It should be noted that values reflect the ability and/or morph once it is fully trained which sometimes differs from earlier costs, durations, or damage values. All costs and damage values are without attribute points placed, without equipment, without passive skills and without champion points so it's easier to compare skills without concern for gear/build differences. Remember that if a skill costs Magicka, it scales with your maximum Magicka while if a skill costs Stamina, it scales with your maximum Stamina. Synergies and Ultimate abilities scale based off Magicka or Stamina, whichever is greater.