Icy Wind actually does not guarantee the OHKO on Salamence w/o SR, though an 81% chance is still pretty good:
252 SpA Keldeo Icy Wind vs. 0 HP / 0- SpD Salamence: 320-380 (96.67 - 114.8%) -- 81.25% chance to OHKO
That's on Naive Salamence, though, so I can only imagine what it would be like against Jolly Salamence.
I don't think HP Ghost is needed (HP Ghost on the Scarf set doesn't 2HKO Jellicent anyway, but it's better than nothing), but I'm not completely sure.
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