Fetch Lands

Fetch lands are, to some, even stronger than true duals. They let you pay 1 life to search your library for a land with the named basic land type. Cycles like Triomes and Shock lands are so good because of the existence of fetch lands. A single fetch can operate as a 5-color land with enough fetchable triomes in your deck. Originally printed in Onslaught and Zendikar, they're the gold standard of mana fixing.