I chose this music because both title and lyrics fit Lei Shi perfectly.
Look cute, talks cute, is adorable ... and MELTS YOUR FACE !!

Her debuff is brutal : +12% Frost damage taken, per stack. She casts faster the lower her health is, debuff ignores invincibility, she continues casting while in Hide phase ... Lei Shi's a monster truck. Killing her will require a near-perfect pull and a full knowledge of mechanics.

She will transition at 80, 60, 40 and 20%, each time becoming invulnerable until you've killed an add.

Engage with full CDs, notice how I bring her down to 70% before first transition. Kill the add as fast as possible, then AT and bring her to 60%. Kill the second add before AT runs out. Then comes a tricky part. If her first phase is a Hide, you're doomed. Die and come back.

If she casts Get Away!, just be sure you destacked before nuking. Use Mirror Images just before 40% transition and Blink (debuff is applied in AoE). Kill the add then IB to go full health. Afterwards, she will Hide.

Here is the INSANE part. Lei Shi is technically level 93. Meaning she can miss you. Now, hang in there. She has to miss you enough so you destack. I'll spare you the calculation : she missed 7 TIMES IN A ROW on my down. I had countless pulls where she would miss a few times the refresh the debuff 1s before is falls off. Hide phase is really long to get out of (only Arcane Explosion works). You can use a Battle Horn to figure out where she is.

Afterwards, it's just a nuke with full CDs.

Patch 6.1.2, 699 ilvl, 3.43% Leech

Music : RedMoon & Meron Ryan - Heavyweight [NCS Release]
https://soundcloud.com/nocopyrightsounds/redmoon-meron-ryan-heavyweight-ncs-release

Armory : http://eu.battle.net/wow/en/character/hyjal/Araitik/advanced

Enjoy :)