Prototype Gateway

When this permanent enters the battlefield place "
Gate" counters on it equal to {x}. During each of your Upkeep steps add 1 "Gate" counter to this artifact.
When this artifact has 5 "Gate" counters, sacrifice it
and search your library for a creature, artifact, or enchantment that costs {5} or less and cast it without paying its mana cost.
When you play a legendary spell, add "Prototype
Gateway" to your hand from the graveyard.