Ryuugi's The Master of Death

The Master of Death by Ryuugi (Also available at FF.Net, albeit not fully up-to-date, under rgm0005) is a Harry Potter/The Dresden Files crossover fanfic.

After a long and fulfilling life, Harry Potter has died. ‘To the well-organized mind, death is but the next great adventure’, as one Justin DuMorne is about to find out. While the other Harry finds his life irrevocably marked by this encounter, Potter soon finds himself trying to find out the truth of his own involvement with the Dresden universe, which involves the headaches of time travel.

This fanfic contains examples of the following:

 * Authority Equals Asskicking: Potter was head of the Aurors.
 * Black Cloak: Rashid's preferred outfit, which gets Potter concerned for good reason.
 * Dark Is Not Evil: We know Ebenezar and Rashid aren't evil, but the amount of dark magic on them has Potter justifiably concerned.
 * Fallen Hero/Tragic Monster: One of the mentioned downsides of being a Legilimens is knowing that people used to be better before their fall.
 * For Want of a Nail: Without having to, Dresden is somewhat better adjusted and gets along better with SI.
 * Humanoid Abomination: Potter due to crossing the universes.
 * Last Second Chance: Potter offers one to Justin and the vampires and is obviously refused.
 * Lethal Joke Character: Potter has a preference for "schoolyard jinxes". Others in his own universe found it weird, but as he notes, they can still stop a dark wizard without needing to resort to Unforgivables.
 * Old Master: Potter himself. Well over a hundred years as head of the Aurors, with an unspecified amount of time actually climbing the ranks, by the time he died and fighting dark wizards all the way makes you pretty sharp. Not foolproof, though.
 * Outside Context Villain: Outsiders are this by definition, but without even going into Potter's specific powers, spells that the Potterverse take for granted like transfiguration are unknown to the Dresdenverse.
 * Portal Cut: Potter uses splinching offensively.
 * Self-Disposing Villain: Both Justin and  make the mistake of summoning the Master of Death and getting Potter, who most disapproves of their actions.
 * Shout-Out: "You see, over my long life, I have seen many strange and wondrous things. However… I must admit, I’ve never met anyone who wasn’t important.”
 * Shrouded in Myth: The Master of Death.
 * Tranquil Fury: Potter a whole lot.