@JoeW Go for it, I don't understand the math well enough to incorporate it into the existing answers. I don't know if it should get a full answer yet though as London Mulligan is still being trialed (so it may change or not be implemented at all).
Just star the message or save the permalink if you want to make it easier to find later though
@JoeW They're playtesting it at an official event, that does not mean we'll ever actually change to it from the Vancouver mulligan across the board, but it's being used at a high level event, that's enough to take it seriously.
There was a quote I saw recently about Legacy but can't quite remember it, something along the lines of:
> Legacy players are accepting of a higher level of degeneracy.
London Mulligan will crank that up a bit in game 1 for Legacy players, but at least in game 2 people will be more likely to hit their sideboarded silver bullets