Changeling is what is called a Characteristic Defining Ability as such it works in all zones the card is found in.
So regardless of what creature type you chose for Cavern of Souls you may use the second mana ability to cast it and make the mirror entity uncounterable.
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Every normal man must be tempted, at times, to spit on his hands, hoist the black flag and start slitting throats.
- H.L Mencken
I Became insane with long Intervals of horrible Sanity
All Religion, my friend is simply evolved out of fraud, fear, greed, imagination and poetry.
- Edgar Allan Poe
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So regardless of what creature type you chose for Cavern of Souls you may use the second mana ability to cast it and make the mirror entity uncounterable.
- H.L Mencken
I Became insane with long Intervals of horrible Sanity
All Religion, my friend is simply evolved out of fraud, fear, greed, imagination and poetry.
- Edgar Allan Poe
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