Shen Long

Shen Long is the wish granting dragon of Earth. The Shen Long of the Black Star Dragon Balls is red, opposed to the Shen Long of Earth who is green. Shen Long can be summoned by gathering all seven of the Dragon Balls of Earth. Shen Long can bestow any wish as long as it does not exceed the power of his creator, who must be still alive (i.e. Kami or Dende).

Multiple times in the Dragon Ball series, Shen Long threatens to kill the summoner if they do not say a wish on time, or if they do not say a wish at all. Shen Long cannot bring back a person from the dead more than once. The Dragon Balls cannot be used for 365 Earth days after a wish is made, as they turn to stone. The Earth Dragon Balls are relatively small, each about the size of a large orange, much smaller than the Namekian Dragon Balls, which are the size of beach balls. The base for Shen Long is a stone statue kept by his creator. If Shen Long is killed, the Dragon Balls turn to stone. The statue also shatters. If the creator or another Namekian wishes to, they can rebuild the statue to give life back to Shen Long and the Dragon Balls. This happened after Shen Long granted Demon King Piccolo's wish for youth.

While Kami and Piccolo weren't merged, Shen Long could only grant one wish. After Dende brought him back to life, he was able to grant two wishes (three if the first does not revive more than one at a time). If the summoner wants, he can only make one wish. This makes the Dragon Balls turn to stone for only six months.

(Source: Wikipedia)