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Harry's patronus is a stag (the same as his dad's)

Harry's partonus memory wasn't really a memory at all. He imagined himself sitting with his parents and just talking. He saw his parents in the Mirror of Erised and just wanted nothing more than to be a family with them.

EDIT: In the book, the memory that works for Harry was when he found out he was a wizard and would be leaving the Dursleys to attend Hogwarts.

Harry called up other memories to cast his patronus such as thinking of his friends being there around him in the midst of the battle.