Got a small update on Ash's Gible. Turns out the mystery move was in fact Rock Smash, not Slash. Look under "Ash's Gible" and it shows it on his known moves. Looks like they were right the first time when they said his known moves. This makes Gible the second Pokemon Ash owns to know an HM Move (HM06, to be exact). And if you look under the trivia, both Grotle and Gible know HM Moves that have the word "Rock" in its name. Pretty cool. No wonder Empoleon took bit of a hit when Gible first used Rock Smash against it (back when he was wild). And no wonder when it struck Empoleon that time, the boulder that Empoleon broke with Drill Peck broke even further.
On a side note, I hope that if Gible evolves, he'll still think he's a Gible and not a Gabite, and continue the head biting stunt. =D