At worst, you can phase out up to five permanents in a dedicated phasing deck
If you get nothing off the triggers, you're probably already in good shape
0.888 per cent (5th card probability rate, regular pack) Immersive Charizard EX (Charizard Pack) 0.222 per cent (4th card, regular pack)
But in at least 75% of situations, I've found the right play is to lead with the Vial, as what you lose on turn two is immediately made up for starting just one turn later
A second mulligan means drawing seven again and placing two on the bottom, keeping five
Landfall Retreat to Coralhelm is one of the best actual landfall cards ever printed and would be a slam-dunk inclusion here, but I also really love slightly different cards like Cosima, God of the Voyage and Trench Behemoth that do a lot of heavy lifting when lands are entering the battlefield with frequency