I made many mistakes, and I didn't do the math to see how many teeth one can collect during this event, but,
the secret seems to be in: 1st Always choose the right deck (the one recommended by the game) and 2nd
Always switch the card in your hand and choose the best possible option based on what you are facing.
So what you really don't want to do is to take more damage than needed, because life goes down pretty quickly, so
always switch to a better card when you see that you can't kill an enemy card from one shot or when the enemy is having a card that deals bonus damage to yours, again switch, but don't overkill your enemy either, keep your best cards for the tougher/latest minions.
And what you always will want to do is to buy almost all the Ability Cards, which are like some spells, in the sense that you can use them to heal, heal and do damage, or just do damage and kill an opponent card without taking any damage at all, which for this reason alone and especially against boss/tougher opponents (with high attack and/or health) are very good.
Thief is extremely good against the boss, for stealing twice as many (golden) keys, or for getting 2x the Epic Halloween 2023 SK. Switching almost every hand and buying health and/or Ability Cards cost me ~ 6-700 teeth, I didn't do the math to see how many teeth are we getting this event but about this much it costs to defeat the boss, and if you don't have that many teeth, it's better to just not spend any at all, either you go for the boss or if not just do as many free rounds as you can each and every day.
Once you get the hang of it, you will see, that the game is pretty easy and actually really fun, congrats to Inno for coming up with something new and challenging this year