A searchable land that provides two of the deck’s primary colors without any drawbacks. In this list, Underground Sea tends to be the primary fetchland target.
Which means that its best to pair Underground Sea with its complement which would be Taiga &mash; a prominent secondary land. When having both lands in play, all four colors are available which makes gameplay much easier.
A perfect example would be that Abrupt Decay can be cast off of this dynamic duo on the end step, untap, and then being able to win the game while having all of the necessary resources.