DARK DESIRE
Your character’s innermost desire can only be described as vile or evil;  to possess some unimaginably powerful thing, to seize power for cruel purposes, or perhaps even to bend the laws of nature and invite a dark power into the world.
[3 Pts.]
This is not an idle fascination for your character;  it is the core of his very existence, a black secret that he shares with no one. At all times, your character is pondering, scheming, seeking information, and carefully moving himself in what he believes to be the proper direction for his goal. It’s not so much that he’s working in opposition to the plans of his “friends and allies,” it’s that he considers them ultimately superfluous;  tools to be used and discarded when necessary. Although your character is infinitely patient, at the very end of his quest, when the goal is in sight, there is no betrayal he will not make and no bond he will not forsake to grasp what he has always desired.

Special: If your character attains his dark desire, it won’t happen after a month or two of adventuring. It will happen after years, or, more likely, decades. The attainment of a dark desire will almost certainly turn your character into an antagonistic NPC under the DM’s control, so it is essential for full dramatic impact that this flaw be kept as utterly secret as possible.

Limitation: This flaw may only be selected with explicit DM approval, due to the fact that it plants a long-term antagonist in the middle of the player-characters, who are usually presumed to be heroes. Is it compatible with a good alignment? Ha! That’s a good one.