400 damage, Avalanche does 50, Times Two because of getting hit in the same turn, Times four because of Salemence's 4x weakness to ice, being dragon and flying.. so 100x4=400.
Well, the reason I called out Swampert next was so I could use avalanche and possibly OHKO it. Since Avalanche is a phisical move doing 400 damage to Salamence... But it was too slow.
I still don't think that would have killed him honestly. >.< It would have done a smidge more. Since Flygon is on the physical side of the spectrum, DM isn't all that great on him...
I know this from experience as I have a Choice Scarf set with that move. xD Dragon Claw does just a little less.