Entry Requirements:

Blood of Amber at 17 (typically part of the Amber Royal species keyword), but can be picked up by most anyone as a 'gimme' at 13, then raised.

Species or Homeland:

Typically, the Amber Royal species keyword, but not a requirement (see above). Becoming a Pattern initiate requires, at some point, access to the Pattern itself, which in turn is often associated with the City Of Amber? or Amber Castle? homeland keywords (especially for possessing initiation prior to play), but again, this isn't mandatory (especially for in-game initiation), provided there's some other viable explanation.

Abilities:

Typical abilities associated with this power include:

      Pattern Devotee *or* Pattern Initiate, History of Amber.

Virtues:

Hmm. This is toughie. Perhaps the Pattern brings out a certain megalomanical tendency? Machiavellian behavior? Maybe that's just the nature of folks who're willing to risk their lives to gain power. You're Campaign May Vary.

Affinities and Feats:

• Movement
  • Shadowwalk/Hellride
  • Track Others
  • Walk the Pattern
• Probability
  • Alter probability
  • Modify Shadow (obviously needs an extensive resistance chart)
  • Shadow of Destiny (usually resisted directly by the target)
• Defense/Perception
  • Blood curse
  • Sign of the Pattern
    • Advanced with prereq: Pattern Lens
  • (Un)Block the Way

Secret:

This secret would probably be something along the lines of making one's own Pattern. Typically, this would require 1W2 ratings in all three affinities, and access to the Jewel Of Judgement?. YCMV.

Disadvantages:

Everyone you love wants you dead? Not sure about this one.