Ice E Mascot was added in Beta 50.0. Previous Versions can be found here.
Ice E Mascot, when played, will choose a random Rare monster from your dustpile and move it to your hand. If you don't have any Rare monsters in your dustpile, it will choose one from your deck instead. If you don't have one there either, the effect fails.
This makes Ice E Mascot usable in a deck that uses cards like Starwalker and Starwalker Bird, which have effects that require the user to not have Rare and Epic cards in their deck. Ice E Mascot allows them to use at least Rare cards, and use this to get them out of the deck as soon as possible so the others can be used.