In reply to Fredt:
There's a 25m slight descent from the summit cairn before reaching an obvious nick from where there are 3 option:-
Easiest is dropping leftward on the Coire Lagan side by slabs, a bit slick in the wet but not bad after first couple of meteres, for 50m to gain the top edge of the scree slopes; grade 2 with use of butt). Traverse this easily for 100m to reach the pinnacles in Bealach Sgumain just before the re-rise to the Bad Step.
Better but harder both to climb & find is the fine narrow crest heading direct from the nick. Ascend a few metres then descend the crest direct (very very greasy in the wet!) until just before the impassable steep drop. Turn this on the R, Coire a' ghrunnda, side by a 15m descent, exposed descending traverse around ledge to below the impasse, slight re-rise up a 5m slab then finally round to the pinnacles; great fun when dry at grade 2/3 as Noel says.
3rd option is to turn this crest on the Ghrunnda side all the way. Drop R from the nick for 10m before following a fault around to the left. This immediately leaves you at top of a steep chimney which has to be descended for a few meteres before regaining the traverse line that joins the "normal" direct line after 50m. Very intimidating 2/3.
Gordon's memory of the Bad Step (or mauvias pas- bad way!) is not wrong. To his description I'd add the lack of easy anchor for belaying, no gear, single finger swap while on impending wall and real barn-door feeling. There is a solid anchor above to belay from which is a good job as 50% of the folk I take there come off! It is also possible for fingery wall climbers to stick more to the crest on the left which is a lot more in balance but still bold. Option round to the left is a loose nightmare.
Finally, worth saying that the SW Ridge of Alasdair approached by either the chimney or Mauvais pas is on of the finest in the Cuillin, even if the blocks look highly improbable at times!