It's a Stage 1.
For a Water and a Double Colourless, he does 50 and the Defending Pokémon can't attack. It 2-shots Donphan and if Donphan wants to attack, he'll have to switch out. That'll be hard for 'phan because of his massive 4 retreat cost.
^ I couldn't be bothered to list it >_> sry
Cryogonal - Water - HP80
Basic Pokemon
[W] Icy Wind: The Defending Pokemon is now Asleep.
[W][C] Ice Ball: 30+ damage. If the opponent's Acitve Pokemon is a Fighting-type, this attack does an additional 40 damage.
Weakness: Metal (x2)
Resistance: none
Retreat: 1
You HAVE to run beartic with Vileplume or else it does not work. The problem is that Donphan is extremely versatile. It's almost never run alone. That's the problem with countering it; you may counter Donphan, but they'll just use an alternate attacker and wreck you.
I think mostly at nationals this year donphan was mostly run with machamp and or yanmega/magnezone. It would be tough to counter combos such as these