"BY THE POWER OF RAGNAROS" is the voiceline from Emperor Thaurissan so your cards in hand will be reduced by 1 mana at the end of your turn.
Tip 1. Mana reduction mostly encourages OTK (One-turn-kill) decks. Drawing cards allow more reduction on cards.
Tip 2. The game usually ends around turn 5. a) When you construct your deck, cards with 5 or more mana cost are not recommended. b) Also mulligan for your key combo cards for your starting hand. c) The most important rule of this brawl is that "Always calculate how much damages you have in hand." If you miss one turn, your opponent can complete OTK faster than you do. d) Loatheb can delay spell combo deck as a tech choice.