Elephant

One time a great devotee of Ganesh was visiting the king of Puri, but was reluctant to visit Lord Jagannatha's Temple as his principle was to only worship Sri Ganesh. Lord Jagannath is non-different than Lord Visnu, Who is the origin of all devatas. This pilgrim was coaxed by the king, who finally persuaded him to visit the temple. It was snan-yatra day, and as he stood before the Deities he asked Lord Jagannath, "If You are what they say You are, Daru Brahman (wooden Brahman), then kindly show to me that form of Ganesh, whom I worship." Deciding to bestow His causeless mercy, Lord Jagannath with Balaram transformed Himself into the form of Ganesh, to the great astonishment and delight of His most fortunate devotee.

http://tirthayatra.org/the-mystery-behind-ganesha-vesha-of-lord-jagannatha/