Abilities
Willump's attacks deal area damage and grant attack speed and move speed to an ally.
Willump bites a target, dealing damage and healing himself.
Willump rolls a growing snowball that damages and knocks up enemies on impact.
Nunu throws snowballs that damage enemies; Willump roots champions and large monsters hit by any snowball.
Nunu & Willump channel a blizzard, slowing enemies in an area before dealing heavy damage.
Guide
Play as a disruptive tank/initiator, using your snowball to poke and your ultimate to control teamfights, while peeling for carries with slows and knock-ups.
Tips
Use your W (Snowball Barrage) to poke enemies from a safe distance and slow them for easier engages.
Maximize your passive (Call of the Freljord) by chaining auto-attacks and abilities to boost attack speed and damage.
Save your ultimate (Absolute Zero) for teamfights or to zone enemies off objectives like the health relics.
Build tanky items like Sunfire Aegis or Force of Nature to survive longer and disrupt enemies in ARAM's tight lanes.
Coordinate with your team to use your E (Snowstorm) for quick engages or escapes over walls.
Combos
W (Snowball Barrage) -> E (Snowstorm) to slow and gap close for a gank.
R (Absolute Zero) -> W (Snowball Barrage) to maximize damage while channeling your ult.
E (Snowstorm) -> auto-attack -> W (Snowball Barrage) for a burst trade in close quarters.