Vernal Equinox
Flash as a keyword had not yet been codified when this printed, so the design names the effect the long way: creature and enchantment spells gain the timing rules that would later be called flash. What makes the line tick is that the permission is universal. Both players get the window, which means the card behaves less like a private ability and more like a temporary change to the game's clock. Green, the color most boxed out of instant-speed interaction, suddenly gets to deploy its permanents on the opponent's end step and during combat, holding mana open the way a control deck holds up counters. But the same allowance belongs to the opponent in equal measure, so the advantage flows to whoever is actually built to act last rather than to whoever cast the enchantment. That open symmetry is what keeps a four-mana "everything has flash" effect from breaking the game: it does not favor its controller, it favors better positioning. Later cards (Leyline of Anticipation, Vedalken Orrery, Alchemist's Refuge) chased the same timing-shift idea from different angles, most of them narrowing the scope or making the effect one-sided. This is the earliest, widest, and most communal version of the line, an open invitation to play the entire creature-and-enchantment half of Magic at instant speed for as long as the enchantment survives.
