Best pranks to do to people on the mountain??

Barefootin_Fiendi would go as far to say that anyone who pulls a "prank" on the hill to someone who isn't a friend is a raging douche bag, and it's a good way to get your ass beat.

I once got pegged from the ground up to the lift by what was basically a large rock covered by a small amount of snow. I didn't have my gloves on and was on my phone and managed to backhand it before it hit me in the face. Two years later and I still have a scar from where it cut my hand. The dumbass that threw it didn't consider that I knew the lift I was on was the only way back up from where he threw it. I waited at the top and with the swipe of a leg he was off balance, face down in the snow, and I literally sat on him and rubbed his face in it until he cried. (He was at least 18, likely 20ish)...

Kids, don't put rocks in snowballs...

spraying randoms is fun, more fun when you get chased
a really big one was kicking out someones boot from the binding, until I exploded a kids binding and he cried.
throwing snowballs at people in hottubs