Metamorphosis

This card can be used in many ways. If you use a card like Change of Heart or Brain Control (But not Mind Control) to take control of an opponent's monster, you can use Metamorphosis on that, as long as you have a monster with the required level in you Fusion Deck.

You can use this card with Magician of Faith, or even the Goat Tokens formed with Scapegoat, and Stray Lambs, to bring out Thousand-Eyes Restrict.

Other good examples of cards to being out are Fiend Skull Dragon (5 Stars), Cyber Twin Dragon (8 Stars), and Gatling Dragon (8 Stars).