Fanir, Wintermourn Rider

Flying, first strike, lifelink, deathtouch
Breath of Wintermourn-Whenever this creature
deals damage to an opponent or planeswalker,
each opponent gets a frostbite counter. Then,
double the number of each kind of counter on
each permanent and player. Remove all frostbite
counters at the start of your next turn. (During
each player's untap step, that player chooses a
permanent for each frostbite counter they have. Those permanents don't untap.)