I was thinking about having the main villain in a high-level campaign be a 12th level bard / 10th level Chronicler
He is the leader in a guild of assassins and uses the Epic Tales ability to give his followers his performance buffs during combat without him actually having to be there.
The Deadly Performance ability kills someone through either joy or sorrow. One of his main ways to kill people involves using his Deadly Performance ability with his Greater Epic Tales to basically send a letter that kills whoever reads it. Basically, a short anecdote or profound truth that causes the reader to die of sorrow, kind of like the movie the Ring.
Is this use of Deadly Performance with Greater Epic Tales feasible? Also, would the letter radiate magic?
Epic Tales and Greater Epic Tales are (Su) meaning supernatural rather than spell-like. As supernatural abilities are in the Magic section, yes, Detect Magic would detect it (3 rounds to locate it normally). While an ability is active it is magical. Once the ability is withdrawn the object it was attached or associated with loses its magical aura (duration is Class Level days for Epic Tales but "Once activated, an epic tale’s magic is consumed.").
My advice is to ensure the leader of a guild has several class levels in the profession/craft the guild represents.