In Double Battles, you can have Smeargle copy the move your ally is using. In this case, if you have a Pokemon with Sheer Cold, you can do a double battle - First, the ally uses Sheer Cold. In that same turn, Smeargle uses Sketch, and your Smeargle can permanently use Sheer Cold.
Note that in Doubles or Triples, the ally must move right before Smeargle in order for Smeargle to Sketch the ally's move.
Source: Knowledge.