So, while snooping around the interwebs, i found something regarding Smash. We know Sylveon isn't fighting, is super effective to ice, and weak to poison, if we are going word for word. R_N has already pointed out what it isnt, but lets go further...
What we know is it isn't any of the other eevee types, so normal is shot. it was easily captured by fighting types, so we could argue that its SE. looking at the chart, they include Steel, Rock, Dark, and Ice. We cut out Dark and Ice already, so skip those. Poison worked on it, so it cant be Steel, and by that, it cant be Poison. All we have left is Rock.
.... I think you see it already.
But lets say that fighting isnt super effective to Fighting. we still know that it isn't Fighting, Ice, or Poison. It broke Ice, which means Fire, Rock, Steel, or Fighting. Same problem, we still have Rock.
But now the nail in the coffin. I'm not sure 100%, but I believe that they said the flower was SE. Poison is SE to one type only, Grass. Minus the eeveelutions, and you get nothing.
Now, even if Poison isnt SE, we would still have Rock. Now call me crazy, but I can say without a doubt that fluffy over there is a Rock type.
New type confirmed from process of elimination.
-drops mike-