I totally think we ought to give an auto-Taunt ability to a Mega. Not sure if Spiritomb would be a good candidate, though.
EDIT-- In fact, MAYBE it is. A Garchomp-esque pokémon (high speed and offenses, decent bulk, setup move) with this ability would be too strong, as it would disrupt stall beautifully AND stop other setup sweepers. On the other hand, a defensive pokémon would be interesting as it would be a nice addition to stall stopping the same targets, but contributing to a more decent paced game (against stall) or slowing down the game for its team (vs. setup offense).
But maybe it would make the metagame too stall-oriented. Hm.
Maybe a more Flygon-esque (no setup move, kinda decent bulk, passable offenses) pokémon, then. More of a pivot than anything else.