Mishra's Mine

{t}: Add {c}.
{t}: Add {c}{c}. This mana can't be spent to cast nonartifact spells. Activate only if you control a
Mishra's Tower and a Mishra's Power-Plant.
{t}: Target Assembly-Worker creature gets +1/+1
until end of turn. If you control a Mishra's Tower
and a Mishra's Power-Plant, it gets +2/+2 instead.