Update: Breaking solo adventure with Sn1p-Sn4p. Finally got my Arthas, Paladin alternate hero after beating The Lich King (with the help of the Sn1p-Sn4p combo). Deck lists in the comments section. :
The Lich King - Hearthstone Top Decks
LICH KING CHEAPEST STANDARD DECK !!! Works for 6+ of 9 Classes ! - Hearthstone Decks
How to beat the Lich King with all nine classes in Knights of the Frozen Throne - Dot Esports
Super cheap decks/guide for the Lich King fight! (all 9) : r/hearthstone
The Lich King Boss Guide - The Frozen Throne - Frozen Throne Adventure - Guides - HearthPwn
Top 10] Best Hearthstone Cheap Decks That Wreck Hard! (June 2020) | GAMERS DECIDE
The Lich King Boss Adventure - Aggro Murloc Rogue Deck List Guide - Hearthstone Top Decks