1. relic of kings always give only 2 spells: a, set your health to 40, or b, shuffle all minions into both decks. this is clearly not balanced, but because the pre-release brawl only uses core cards and new expansion cards, the mechanics check out.
2. similarly, scrappy scavenger has a very high chance to discover fyrakk when you have 9 mana left, and discover bob the bartender or blizzard when you have 6 mana left. between those and primordial glyph, Q’onzu and scoundrel, you almost always have on demand freeze.
3. even the imbue paladin match-up is not too difficult after you practice a bit, because you can often just freeze their board and win. The murloc paladin match-up is a free-win, games usually go like this (happens to be my 6th win game)
4. five-mana location wins games. vs control, you can burst them down with +2 attack, vs aggro like DK, it comes online one turn before your 6 mana stall
5. focus on spell discovery before quest completion (if you have a choice between the two), because minion discovery is much much more effective after quest completion.
6. Q’onzu is so good when used right. you can eliminate a critical draw of the opponent sometimes (at 3 health against murloc paladin? give him a spell to prevent top-deck weapon lethal)

More details: https://www.reddit.com/r/CompetitiveHS/comments/1lq5oil/guide_to_easy_6_wins_with_mage_in_prerelease_brawl/