The Puddle Jumper

Whenever The Puddle Jumper enters the battlefield, create a colorless artifact token named Gold. It has "Sacrifice this artifact: Add one mana of any color to your mana pool."
{0}: The Puddle Jumper gains flying.
{0}: The Puddle Jumper loses flying.
When a player casts a spell or a creature attacks, exile The Puddle Jumper. Return it to the battlefield under its owner's control at the beginning of the next end step.