Apart from rock smash, it comes with earthquake too. So, considering its type advantages it could be a great electric type killer. But electric types aren't much of a challenge anyway. Water type outclases it for potential rock type kill. Anyways, apart from it's miserable dual type, it's a great attacker if you dodge.
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Rhydon with Rock Smash
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Agreed. In theory, Rock Smash has a type advantage against Normal mons (Snorlax), but the type advantage in Pokemon Go is weak and hence it does not make it better than Mudslap (but it's pretty close against Normal).
Mudslap is also more versatile and combine well with Rhydon's type (against Electric especially and Fire).
Rock Smash is serviceable (esp against Normal types), but Mudslap is better across the board. At 2000 CP, I would try it out against Snorlax until you get Mudslap.