Format Legalities
Format:
Block Constructed
Standard (T2)
Extended
Modern
Legacy
Vintage
Commander (EDH)
Legal:
Official Oracle Text
As Cavern of Souls enters the battlefield, choose a creature type.
: Add 
to your mana pool.
: Add one mana of any color to your mana pool. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.
: Add to your mana pool.: Add one mana of any color to your mana pool. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered. 
Official Rulings
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Author: Auburn200925
Comment:i love this land
Author: Jguberman
Comment:Isn't this a little TOO good, for every format?
Author: Gamma345
Comment:Great. Now My Black/White can run the Legendary Angels without running any more colors