Hello, pay up to pass... a reasonable fee of ALL your gold will do! Heh heh!

Fire go brrr. Use each avatar as needed to give yourself as much card advantage as possible:

Pathfinder: You will always want to put on her mask. Turn 4 will almost always be "Pay 3 to become pathfinder, tap for my fourth site". Use pathfinder to continually draw spells at the start of each turn while keeping on curve for mana.

Sorcerer/Interrogator: Once you hit 6 sites, transform into one or the other to keep up the card advantage. You'll probably have to pay life and be behind the first turn or two, but that will be obsolete in a few turns when you still have 5 or 6 spells to choose from each turn. Use sorcerer by default, start as (or swap to, if damaged) interrogator if you have a healthy number of minions on the board.

Flamecaller: Your finisher. Pay 3, tap to launch the final blow. Straightforward, you really should only use this guy as your game ender.

Ironclad: Start off on the back foot? Pay a little too much life for minions and now things look desperate? Ironclad is your defensive play, lowering your incoming damage when needed. Golden harp is a fantastic play if you still have Ironclad available to swap into (also helps with greater blood demon's cost). The avatars above are your main plays, this guy is your plan B if things aren't going well.

Necromancer/Witch; When you need to coast for a bit - when you can't be sorcerer/interrogator, or if you have a healthy advantage or a decent sized hand, these guys will help give you options while you fill the board. Witch can help keep the opponent behind on mana in the mid/late game, or help chip away at their health while your minions are fighting theirs. Paying 4 to summon a chump blocker doesn't feel great, but can be the difference between a win or a loss. Paying 1 for a skelly every turn after changing though, that can be pretty nice.

Hey Bear, hey! This guy gave us all his gold! What a sucker, right?