I remember a one-shot, probably part of a one-shot and abandoned starts collection, which had Corwin confronting Dumbledore in his office on Harry's behalf, but it would be hard to find it. The is more of a Buffy the Vampire Slayer cross - when Xander goes on his road trip, he manages to acquire Amber genes and picks up Sirius Black, who showed up there when he fell through the Veil.?
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