If you’re looking at a hand-carved Krampus mask, I’d pay particular attention to the weight. Some have real horns and are quite heavy. That might be a bit impractical as a Christmas present for your grandson, especially if you have to carry the mask home in your luggage. I’d also ask the professional carvers whether they even have any ready-made masks available to take away.
You might want to have a look at the private listings on Willhaben. With second-hand masks, I’d ask about the padding and fastenings on the inside.
Or the little Krampus figurines from Minikrampus in Hof near Salzburg. If it doesn’t necessarily have to be a mask to wear. They’re intended more as decorations.