The power-up used to be an Anvil, but it was replaced with a Hammer in the final version.
A telepod was supposed to be available in December 2014 to unlock an additional costume for Poppy (Spring Day costume), but it was never released. While the costume art is finished, the related photograph is unfinished. Two other costumes for Luca are unused, such as a black beanie and a yellow afro wig. These can be found in the game files.
Unused Spring Day Poppy Photo
Spring Day Poppy and telepod base
Spring Day costume for Poppy
Yellow Afro Wig costume for Luca
Black Beanie costume for Luca
Chapter 3 and Circus level
After the release of Angry Birds Stella, a third, unnamed episode was teased at the end of the game's second episode that says "Coming Soon", same goes to Circus level in v1.1.1 update. But unfortunately, both of them were scrapped as the game was discontinued.