If an effect allows a player to cast a spell as though it had flash only if an alternative or additional cost is paid, that player may begin to cast that spell as though it had flash.
April 27, 2018 · Dominaria
If a spell would have flash only if certain conditions are met, its controller may begin to cast that spell as though it had flash if those conditions are met.
January 19, 2018 · Rivals of Ixalan
If a spell would have flash only if certain conditions are met, its controller may begin to cast that spell if those conditions are met.