Skull Fossil

A Skull Fossil is a fossil that resurrects Cranidos. The Dream World Skull Fossil bears a resemblance to Cranidos's head.

https://vignette.wikia.nocookie.net/pokemon/images/1/1f/Dream_Skull_Fossil_Sprite.png/revision/latest?cb=20110524003109

How to obtain

 * 1) Go to Eterna City and gain the explorer kit from the man in the house next to the bike shop. You must then use the explorer kit to go into the Underground.
 * 2) Once in the underground you must mine the walls; however, to get a skull fossil the last digit of the trainer ID must be odd. If it is even, the chances of mining a skull fossil are rare.