Mega, Vastforge Overseer

When you cast Mega, for each time it's been cast
from the command zone this game, add
{c}{c}. This mana doesn't empty from your mana
pool as steps, phases, and turns end. Spend this
mana only to cast nonlegendary artifact spells.
When Mega is put into the command zone
from anywhere, search your library for an artifact
card, reveal it, and put it into your hand, then
shuffle your library.