You can't get the move rock smash in Pokémon Yellow version. The move does not exist. It was introduced in Gold and Silver.
Trough eterna city
You can get clefairy in 2 ways: 1. First you need a ditto and a cleffable. Then you put them at the day care. After a while of walking around, there will be an egg. When it hatches it will be a cleffa. You can level it up until it is a clefairy. 2. You can trade clefairy from Fire Red or Leaf Green onto emerald.
go to top of mt. coronet capture dialga go to sunyshore city and you can get in
I've played this game over and over and never remember needing to find my rival in Mt. Coronet. If you're in the part where Prof. Rowan tells you that you should check on your rival, head up to Snowpoint city. Go thorugh Mt. Coronet and you should find yourself in snowy route 216 when you exit. Sorry if this doesn't answer your question, but I know for a fact that you never have to find your rival in Mt. Coronet.
From Oreburgh city
There are Diffrent Entries to Mt Coronet,one leading from Oreburgh City,and one from Celestic City and Entrna City.
first go to oreburgh city then go to mt coronet i can say that will 100% work
go to the cave from jubilife city not mt. coronet near oreburgh city talk to the hiker and you will get rock smash
there is only one mt coronet but there are four entrances. you can get to the top of mount coronet through the oreburgh entrance
In pearl the first legendery Pokemon is PALKIA, and it is in the SPEAR PILLAR. You get there from MT. CORONET from oreburgh city entrace.
You need to travel south on Route 206 in Pokemon to get to Route 207. It connects with Oreburgh City and Mt. Coronet.
Mt. Coronet is between Oreburgh and Hearthome. It is also between Eterna and Celestic.
you need rock smash and/or strength to get through the mountain............ you need to beat the oreburgh gym for rock smash
The ground or Earth plate is in Mt. Coronet on the west side of Oreburgh City. It's downstairs and you need HM Surf to reach it.
Mt. Coronet is located in the Sinnoh region in Pokémon. It spans the five routes: 208, 207, 216, 217, and connects Celestic Town, Eterna City, Oreburgh City, Snowpoint City, and Hearthome City together.
i think you get it from dawn far left of mt. coronet (the one near oreburgh city) but u can only get it if u never been to the far left of mt. coronet. u also need a bike to get up the brown slope that leads u there