Tails, High-Flying Genius

Flying, Vigilance
When Tails, High-Flying Genius enters the battlefield, if it was cast, create a Legendary emerald artifact token named Yellow Chaos Emerald with "When Yellow Chaos Emerald enters the battlefield, mill a card for each emerald you control" and "Artifacts cost 1 less for each Emerald you control"
{t} an Emerald: Create a 0/0 Construct Artifact Creature with "This creature gets +1/+1 for each artifact you control".