What is the rock in Pokemon emerald

Well, actually, it depends on which rock you mean. If you mean the "wiggly rock" at the battle frontier, then that's actually a Sudowoodo, and it attacks you when you water it with a wailmer pail, giving you access to Artisans Cave, filled with Smeargle, a Pokemon that copies the first attack that you use against it. Other rocks are either smashed by rock smash of pushed by strength.