The October 2016 bug fix listing says "Some festive knit items are now more effective against cold, thanks to Arkaim for the suggestion." Arkaim can probably tell more, but here's a list of thematically cold themed techniques to test?
This may or may not be the same as the "Christmas Spirit" flag already on the wiki. Also to test: festive knit hat, knit cap, etc.
Frost Breath
Gnarled Claw w/ Frost Breath
Pyrophobia w/ Cold Skull
Lethal Resolve w/ Cold Depths
Coin Flip sometimes
Razor Snowflake?
Project Skull vs. Etheric
Snow Blade
Prison Of Ice
Whiteout
Blade Of Frost
Snow Maiden
Stalk Through Snow?
Watery Passage?
NPC:
Ball Of Slush
Burst Of Slush
Construct Snowman
Drift Straight Through
Envelop In Slush
Fill With Frost
Frost Touch
Handful Of Snow And Ice
Ice Lance
Ice Shatter
Icicle Fangs
Icy Tendrils
Pile On?
Plow Over
Pull to Darkness
Roll Over
Strange And Terrible Whispers?