This one could actually rival the Tale of the Spooky Squash in terms of difficulty, if only because of the constant freezing effects which so many enemies can inflict. It definitely combines the "Boss has incredibly high Health" aspect from The Tale of the Spooky Squash and the "instantly vanquished if you Fail" from A Dinner With Sasquatch.
I've written a more detail tutorial elsewhere but the two key things for this Boss Hunt are to have heal Flowers and Sunflowers with heal beams at the ready since being healed cancels out any Status effect, like a movement penalty or freezing effect.
The ideal situation is for a Sunflower to target a higher damage character with their Heal beam and then drop their own Heal Flower, preferably the Rainbow Heal Flower alternate ability for the constant Sundrops if they have it available. The Sunflower should try to stay back so that the character they are actively Healing gets targeted by the Bosses and the character being healed should try to stay close enough to the Sunflower that the Heal Beam doesn't break. You don't have to chase the Yeti King until you have Super Sunshine Power and it's actually better to stay far away from him otherwise.
You also need to be able to reach the little Snowman tokens quickly to destroy them so that you can avoid Winters Grasp- every time to destroy one you get more time added to give you a chance to get to the next one; breaking up into teams of two where one destroys the Token while the other fends off Zombies can work well.
I was on it just after launch when everyone was still trying to figure out what to do so the random Groups I was put with had a hard time getting very far, especially with newbie players dropping out because of the high difficulty curve but I'm confident that when I group with my regular team we'll knock this one out soon enough.