Alright. So I think I may have something. Completing a dungeon will (always) give you 14 bronze keys, 6 silver, and 6 gold, which are worth 68 progress. You'll also get some more progress for any cards you have left over, but we won't be counting that. Without spending any teeth, you can defeat at least 3 enemies generally, sometimes more. The first 3 enemies give you 8 bronze keys, worth 8 progress. Also, we can get keys from the daily challenges, from which you'll average 62 progress. Lastly, you can use 2 gold keys daily to get the double chest, which gives you up to 252 extra progress (12*21) than if you just spent them normally. You can play 63 games over the event (3 decks, 21 days).
Therefore, the strategy:
- Over the course of the entire event, you want to complete 5 dungeons. This will net you at least 340 progress (5 * 68) in terms of keys. With my current estimate of 5310 free teeth, you'd have to average 1062 teeth per game. Should be possible! Just watch your health, buy extra cards, etc. If you have thief cards, try to use them against the boss!
- For all your other 58 games, don't spend any teeth. Just fight as far as you can until you die. This will give you at least 464 progress (58 * 8) in terms of keys.
- Open the 2x gold box every day with your gold keys. This will use all of your gold keys, unless you get more by using the thief card on the boss. Assuming you don't, you'll get a total of 30 gold keys, which are worth 180 extra progress when doubling.
- Play the daily challenges every day. This gives you about 62 progress.
In total, you end up with 1046 progress, a ton of rewards, and a Lv. 8 Lab. Depending on how leagues go, you may only need 800 progress for the level 8, but I'm airing on the side of caution. Hope this helps!