Can't Catch Me!
Not unlocked yet[2010 Xmas] Kill 2 Christmas Gorefasts with a Melee weapon from behind in one wave.
Toasted Jack Frost
Not unlocked yet[2010 Xmas] Kill the Christmas Scrake with a Fire-based weapon.
That's not Santa!
Not unlocked yet[2010 Xmas] Kill 3 Christmas Bloats with the Bullpup in one wave.
Rudolph, the Bloody Nosed Reindeer
Not unlocked yet[2010 Xmas] Kill a Christmas Crawler with a Crossbow.
Not So Silent Night
Not unlocked yet[2010 Xmas] Kill a Christmas Siren with an undetonated LAW rocket.
Fending off Mrs. Claws
Not unlocked yet[2010 Xmas] Kill 3 Christmas Stalkers with a Lever Action Rifle without reloading.
Who Brings a Gun to a Snow Ball Fight?
Not unlocked yet[2010 Xmas] Kill a Christmas Husk with any Pistol.
Deck the Halls with Buckets o' Blood
Not unlocked yet[2010 Xmas] Kill 3 Christmas Zeds in 1 ZED time chain with a Melee weapon.
Tis Better to Give than to Receive
Not unlocked yet[2010 Xmas] Drop 3 Tier 3 weapons for others (with which they kill at least one Christmas Zed).
Eggnog Anyone?
Not unlocked yet[2010 Xmas] Get covered in Christmas Bloat Bile and live for 10 seconds on Hard, Suicidal, or Hell on Earth.
Bad Santa
Not unlocked yetUnlock 10 of the 13 Christmas Achievements along with any Christmas Map achievement.
Back to Work
Not unlocked yet[2010 Xmas] Kill 20 Christmas Clots in one wave.
Uber Tuber
Not unlocked yetExpensive but delicious! Brought to you by Dr. Dougley and Lord Ned.
Science Got Done
Not unlocked yetWin a Long Game on Aperture on Normal Difficulty.
Still Alive
Not unlocked yetWin a Long Game on Aperture on Hard Difficulty.
This is a Triumph
Not unlocked yetWin a Long Game on Aperture on Suicidal Difficulty.
I'm Making a Note Here, Huge Success
Not unlocked yetWin a Long Game on Aperture on Hell on Earth Difficulty.
Golden Potato
Not unlocked yetGet into GLaDOS' core on Aperture.
Flea Circus
Not unlocked yetWin a Long Game on Abusement Park on Normal Difficulty.
Dog and Pony Show
Not unlocked yetWin a Long Game on Abusement Park on Hard Difficulty.
3 Ring Circus
Not unlocked yetWin a Long Game on Abusement Park on Suicidal Difficulty.
On Top of the Big Top
Not unlocked yetWin a Long Game on Abusement Park on Hell on Earth Difficulty.
Ringmaster
Not unlocked yetKill the "Ring Leader" (Circus Patriarch)
Sparring with a Master
Not unlocked yetKill a Circus Gorefast with a Melee weapon.