Please have a look at Tom Fralich's thorough description of the NW-Ridge and how to reach Pt. 2.687M.
The Mittaghorn Kletterstieg
(Via Ferrata) was created by the mountain guides of the Saas valley in June 2004. The beginnig of the trail starts up at Pt. 2.687M. where a Swiss flag is placed and the sign you can see here above right is put up. This point is clearly seen down from Saas Fee. A good trail is following the ridge up to around 2.700M. From here fixed steel ropes are taking over. Iron steps and iron grips are appearing just where you need them to make your climb easy and safe. Nevertheless spectacular. At one point up at around 2.800M the iron steps takes you up against a big wall. However the robust iron grips are solid as rock!
You need a harness and two carabiner. Preferably a "via-ferrata-set". A helmet and some good gloves are also recommended.
On the top summit, besides the summit log book, there is metal box with a slot where every climber puts CHF 5 for the trails maintenance.
Same route as Tom describes in the NW-Ridge route;
down the east flank and back to Plattjen. (or Britannia hut SAC.)
I do not recommend the NW-Ridge for descent.