This is excellent, @evouga! This was exactly the type of analysis I was hoping to see. Thank you so much for doing this!
@fsecco and @Protoaddct I think that view is a bit myopic. The 5% failure rate was always more of a talking point than a significant detriment for dredge. So the deck lost 1 in 20 games or 1 game every 7 to 10 matches (or basically once an event on average)? Yeah, the London mulligan eliminates the number of non-games, but that was the stated point of the rules change. The important aspect of the above figure is that restricting Serum Powder would have a non-negligible effect on the starting hand size of the Dredge opener. From my experience with and against Dredge, the hardest games to win post board are the games in which Dredge keeps 7-6 cards, which allows it to navigate the hate, and restricting Powder would lower the likelihood of that by it looks like 10-15% or so (for 7 cards). That honestly might be worth considering if the deck proves too strong if the new rule is implemented.
Edit: A 90% chance of keeping a 6-7 card hand with Powder means I'm not cutting Powders from my dredge list. I think they are well worth the increase from 75% (which includes one Powder from the chart).