So basically, I flip for Sand Guard when the effect of damage comes into play, after effects of cards attached have already been figured, and the attack finally "hits" Flygon, the stage that occurs right before applying any Status Conditions that go with the attack.
This came up when my Flygon was hit by Team Aqua's Spheal with Powder Snow. I had accidentally flipped to see if Flygon would wake up before flipping to see if it took 20 damage off the final attack damage. I just wanted to check and see exactly where flipping for Sand Guard would come into play before I go and make another mistake like that.
Thanx for your answer, I suppose this could be closed...