Edit: Any single dark or chaos spell is reflected, by any mage with a mirror, with the probability described in the manual. It seems that Jalib's ability makes the probability of reflection on his own troops minimal.
Vampirism is an interesting spell from a mechanics perspective in Heroes 5. It's a dark magic spell, but it has a positive effect, so it can be "cleansed" by adepts and reflected by mages with a mirror.
I'll add a replay of the Jalib mirror match. It's interesting because it wasn't decided in the first 2-3 turns, but rather quite late in the game. And if the opponent hadn't made a few small mistakes, it would have gone to the endgame.