Well, how I did it was, I picked Olimar, because he can do the up+B to grab the ledge. I jumped off the edge as far away as you can while being safe, floating back towards the edge, then up+B when i was below it. The alloys are too stupid and will follow you off the edge. Plus, when you grab the edge, press A to hit them away. Repeat this immediately and eventually they will die. Watch out, because they can hit you in the air. OR