When are Potion shelf requirements checked during a turn, and in what order?

Question

Accepted Answer

Each shelf's requirement is checked once, at the end of the play phase: after cards are played and acquired, but before the market refills. Shelves are read from the top down, and you cannot go back up to a shelf you have already passed.

Harry Potter: Hogwarts Battle

When are Potion shelf requirements checked during a turn, and in what order?