You can. Changeling is a characteristic-defining ability, which means that it functions at all times while the card is in any zone (or even outside the game.) Mirror Entity is an Elf card (as well as every other creature type) while it's in your library.
Yes you can. Shapeshifters/Changelings are ALL creature types.
Don't fall into the trap of assuming that all Shapeshifters have Changeling.
Shapeshifter is a creature type. Changeling is an ability. Changeling grants all creature types, and all cards with Changeling are printed as Shapeshifters just for consistency (and to have something on the type line), but there are plenty (54) of Shapeshifter cards which do not have Changeling, and thus do not have every creature type. Clone and friends, for example, the various Morphling style creatures, and even Volrath the Fallen and -- surprise, surprise -- Shapeshifter.
If I cast Elvish Harbinger can i fetch for Mirror Entity?
I believe you can't.
Thanks in advance
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Shapeshifter is a creature type. Changeling is an ability. Changeling grants all creature types, and all cards with Changeling are printed as Shapeshifters just for consistency (and to have something on the type line), but there are plenty (54) of Shapeshifter cards which do not have Changeling, and thus do not have every creature type. Clone and friends, for example, the various Morphling style creatures, and even Volrath the Fallen and -- surprise, surprise -- Shapeshifter.
Two Score, Minus Two or: A Stargate Tail
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