Rocky is Emile's Onix in his Let's Play of Pokémon Crystal.
Emile traded away his Bellsprout to NPC Kyle in Violet City for Rocky, who knew Tackle and Screech at the time of receiving him, Emile having caught his Bellsprout for that exact reason. Emile groused, however, about being unable to nickname the Onix Phil instead, and after taking Rocky's Bitter Berry, stored him in the PC Box.
Rocky remained there for the rest of the LP, never seen again.
Emile mentioned Rocky as being particularly useful in the Azalea Gym, since Gym Leader Bugsy's strongest Pokémon, Scyther, had a quadruple weakness to Rock-Type attacks.
Emile mentioned Rocky again as being particularly useful in the Goldenrod Gym, since it resisted Gym Leader Whitney's Clefairy's Doubleslap and her Miltank's Rollout and Stomp (though he mistakenly said Milk Drink instead of Rollout, the post-edit text onscreen remarking that Onix must be a cereal Pokémon).