Knuckles, Emerald Guardian

When Knuckles, Emerald Guardian Enters the Battlefield, Search Your Library or Graveyard For a card named The Master Emerald and put it on the battlefield taped.
non-Master Emeralds you control cost {2}less to cast and have "Equip {0}" for as long as you control The Master Emerald.
You may Cast Emeralds from exile if they have an Echidna Protection counter on them