You will get as many chances as you need to catch Cobalion provided you keep on defeating it in battle. Every time you beat the Champion, it will respawn all Legendary Pokémon that were defeated in battle that weren't caught.
Chat with our AI personalities
Leave and return to the cave and Cobalion will have returned. So then you may capture it. I suggest Timer Balls.
you catch cobalion
yes you get a 2nd chance after you get the national pokedex
There's not a fixed amount of pokeballs needed to catch a pokemon. Though, there are many different strategies to catch pokemon, weakening it to red hp and putting it to sleep works best. (at least for me...)
20%.