Hearthpwn

Context

Welcome to Icecrown, Lich King's home! This is a guide on how to defeat the last encounter with the boss Lich King on the Priest class.
I'm not much of a Murloc/Combo Priest player myself. With the addition of Embalming Ritual in SoU, and the existence of Topsy Turvy I was wondering already if we should expect some 'new' combo. There is still no competitive OTK Priest including the two cards I've mentioned, but plenty of members discovered an infinite damage generator in Singleplayer game modes. This is my list. 

What is Lich King's special ability when against Priest, you might ask?
Shut up, Priest. Yep, it's that impactful.
 

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Summary

You can defeat LK starting Turn 5.
Post-Turn 7 might be more... APM intensive, indeed. However, worry not, you can still win.
How long you draw the Combo Pieces, you can always win.  

What's the OTK Combo?

0. Have at least 5 Mana Crystals.
1. Play Knife Juggler
2. Play Radiant Elemental
Knife Juggler deals 1 damage to a random enemy - minion or the LK.
3. Play Test Subject
Knife Juggler deals 1 damage to a random enemy.
4. Play Embalming Ritual on Test Subject
5. Play Holy Smite or Topsy Turvy on Test Subject
This will kill your Test Subject. He will be resummoned immediately after, with a clean deathrattle. In the process, Knife Juggler deals 1 damage to a random enemy.
6. Repeat Steps 4 & 5 until Lich King dies of boredom enough damage in his face.

Mulligan

Always keep Knife Juggler & Radiant Elemental.
Feel free to keep one card that will help you draw more
This deck isn't mulligan-centred as some others, so feel free to play anyway and simply draw cards until you have the needed cards.

Card Choices

2x Holy Smite
2x Topsy Turvy - Core parts of our combo. For the combo, we only need one (1), however, having four (4) of them simply ensures higher chances to draw into one of them.
Animation-wise, Topsy Turvy's faster than Holy Smite, which is still faster than Forbidden Words.
Alternative: Forbidden Words. It is still do-able if you only have 2x pieces of any of the aforementioned card, but I'd highly recommend against it.

2x Embalming Ritual - A core part of our combo. Unreplacaeable.

2x Test Subject - A core part of our combo. Unreplacaeable. FFS.

2x Power Word: Shield - Nice card to cycle through your deck quicker. Feel free to use it on LK's enemy minions if you don't have any minions or play it on Test Subject as last resort to get one of your combo pieces. Also, it is a Basic* card.

2x Dead Ringer - Nice card to tutor one of your Test Subjects or another cycle card. 

2x Knife Juggler - A core part of our combo. Unreplacaeable. I swear a Flamewaker would have made our life so much better, but we just have to settle for what we've got. Plus it just good buffed back. Yay?

2x Novice Engineer - Nice card to cycle through your deck quicker. Also, it is a Basic* card.

2x Loot Hoarder - Nice card to cycle through your deck quicker. Also, not really a Basic* card.
Alternative: If it screws you too much over the Dead Ringer, remove it and just play some Prize Vendor or Big Ol' Whelp in its place.

2x Radiant Elemental - A core part of our combo. Unreplacaeable. I mean it.

2x Thrive in the Shadows - A great nice card to tutor the Embalming Ritual or Topsy Turvy; this card will improve your overall experience with the deck.
Alternative: Thanks Blizzard we have an arguably better & cheaper version of the Shadow Visions. if the card disappears in a year, Shadow Visions, Mass Dispel or a Mass Hysteria to stall the battle can be your alternatives.

2x Coldlight Oracle - A really nice card to cycle through your cards quicker.
Alternative: Please do not overlook this small guy out, it's so much better to have at least one (1) copy of it. Prize Vendor can be your alternative.

2x Acolyte of Pain - Quite a nice card to cycle through your deck quicker. Also, not really a Basic* card.

2x Sandbinder - Niche tutor card for the Radiant Elemental. The only reason this is here it's because it can heavily improve your drawing experience. Definitely not essential.
Alternative: If you hard mulligan for Radiant Elemental, you will be just fine. 

2x Armor Vendor - Great stalling tool. 
Alternative: Please just include the card. I'm out of ideas, besides Gnomish Inventor, Witchwood Piper or Insight. 

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 I still can't understand the combo...

Credits to Kinky gaming for showcasing this combo.
*He doesn't use this deck

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Best of luck in your quest to get the mighty Arthas! <3

-LeoKing#21786 [EU]