Empress of Winter

The Empress of Winter is the boss of the Event Winter Storm (which I will add to the page later). She appears on any track that takes place outdoors on a randomly selected round between 90-130. Like Gap Bloon and Abyss Bloon, the Empress will override that round.

Yuki ~ Winter's Ruler

 * BGM: Adventures of the Lovestruck Tomboy

In this form, Yuki only has 900 HP. (Low for a boss, right? XD) However, don't be fooled by her low health. In this form, she is a borderline God-d**ned boss! She's technically not a bloon, but a Yuki-Onna, so you don't pop her. She does, however, float at the speed of a blue bloon. Her abilites are...
 * Frostbite: Freezes a random number of towers on screen, stunning them for five seconds and, if it's a monkey tower that is not in a vehicle, damaging them for 10% of their max HP! Ouch! What's worse is that MONKEY ACES AND HELI-PILOTS CRASH when this ability is used, instantly killing them!
 * Snowball Bombardment: Throws as many as 20 snowballs to random targets on screen. The snowballs stun towers (except for vehicles) for 5 seconds. Machines are stunned longer (8 seconds), because it clogged up their firing mechanism.
 * Ice Armour: Freezes the air around her, giving herself a whopping 10 AD for 20 seconds! Yikes! Hope you have some 3-X or stronger Snipers!

Once Yuki's done trolling you (take down the first form), you will be taken to a place that looks like a massive white tower, half-buried in snow. Like other event bosses, your towers will still be preserved here. Just in your inventory. This tower is her home turf. The Tower of the Frozen North.

Frozen World of the Far North

 * BGM: Hiroari Shoots a Strange Bird ~ Till When?

In this form, Yuki has 2500 HP, but, instead of moving around the track, she teleports around the screen. (Like E.N.T.I.T.Y., but less annoying, as she has way less HP.) However, her abilities are still annoying.
 * Frostbite: Same as before, but hits half of all your towers!
 * Weather Control: (Lame name, I know... sto) Using her power over winter, Yuki can call up a randomly selected one from the following weather conditions.
 * Snow: The track snows for one minute. However, it's too cold for any of it to melt, and it snows fast enough to bury a monkey tower in five seconds! Yikes! Also, when a tower is buried, it takes 1 HP damage every second until the snow melts or the tower is destroyed! More yikes!
 * Black Ice: It starts raining (just like in Rain or Shine). However, this rain freezes instantly, covering the track in ice! Bloons moving on the track will all move three times as fast!
 * Sleet: Little ice balls fall from the sky, damaging a random tower by 1 HP every half-second! Ouch! Lasts for 1 minute.
 * Winter Winds: (Always used immediately after Snow) Blows all the snow around, unearthing buried towers, and also stunning them, sometimes burying them again!
 * Warriors of Ice: Spawns in 100 bloons of random rank from White onward!

If you can take Yuki down in this form, you and your towers will be whisked away to the top of the Tower of the Frozen North, where her wrath is like a thousand blizzards...

Heart of the North ~ Blizzard of Ages

 * BGM: Love-Coloured Master Spark

Hoo-boy, you really made her mad this time! Anyhoo, in this form, she has 3600 HP, but flies in circles around the screen as fast as a D.D.T.! Her abilities in this form are...
 * Freeze Ray: (Cliché, I know.) Fires a beam of ice elemental magic at a tower that pierces through it (because it's a laser). It also does 20 HP damage and freezes it, just like Frostbite!
 * Royal Guard: Same as Ice Warriors, but twice as many bloons are summoned.
 * Perfect Storm: ALL the weather conditions from Weather Control are used SIMULTANEOUSLY!!
 * Frostmaul: Basically just Frostbite, but it hits ALL TOWERS and deals 5 HP damage!
 * Lesser Spirits of Ice: Calls up three smaller duplicates of her first form that have 250 HP and surround Yuki on all sides, orbiting her at the speed of a Glaive Lord's glaives on fast forward.

After beating this form, you will cheer as the tower crumbles and the sky darkens and the snow turns blood red... wait, what?

Perfect Winter Storm ~ Yuki's Vengance

 * ''BGM: Locked Girl ~ The Girl's Secret Room

You don't really see one-winged angels everyday. Well, other than looking in awe and terror at her final form, you actually have a task: Knock her down from 1600 HP to none in as little as 3 minutes! This will not be easy, because she regenerates her HP at a rate of 30 HP per second! Oh, and it's nighttime in this form. Better get a M.O.A.B. Assassin up! Fortunately, she just sits in the middle of the screen, flapping her ENORMOUS wings. She has only one ability in this form, but it is a real doozy...
 * Last Days of Winter ~ Wrath of the Angelic Yuki-Onna: Uses ALL of her abilities from the previous form (except for Freeze Ray and Frostmaul. Also, Royal Guard is nerfed to 100 again, but it is all camo bloons!)! Also, she summons minions that travel around the screen, acting like the dupes. However, these move at the speed of a Yellow Bloon! Yikes!

After you defeat her once and for all, you will finally cheer up as the normal colours return, Yuki's massive wings shatter, the sky brightens, and Yuki returns you and your army back to their original map. Yay! Unfortunately, no more epic music unless you have your own. sto

Backstory
Yuki is the kind-hearted empress of the northern lands, with power over winter weather. She is a friend to all living things in there, but her kindness didn't stop her from getting enraged over the destruction of the ozone layer caused by the monkeys and bloons with their industry. Also, global warming was degrading her homeland ever so slowly, and she had to do something about it! So she decided to show both Appire and the bloons the error in their ways. Will she succeed...?

Trivia

 * Well... If you don't know what a Yuki-Onna is... here you go.
 * Oh, and Yuki's name translates to "snow" in Japanese.
 * Her one-winged angel form's wings will look like Eboshidori's Sunyata boss (skip to 6:41)
 * I will add pictures later.
 * No, this will NEVER be put in the Bloons or Event Bloons categories. EVAR.