That depends on it's type. If it's fire type then water is more powerful if it's grass then fire is stronger and if it's water then grass is stronger. The list goes on but those are the basics
Legendary dragon weakness is legend dragons
legendary
No you can catch one of the legendary dogs anywhere in kanto, wich one you will find depends on the weakness of your starter pokemon
Dark Pokemon are Psychic Pokemon's weakness.
It is a rare pokemon, but it is not a legendary pokemon
No, it isn't. Level it to 100, give it Wonderguard since Spiritomb doesn't have a supereffective weakness, a Lum Berry just in case of a Darkrai's certain move, use action replay to teach it any TM/HM, and you'll have an invincible legendary looking pokemon that you can use in Wi-Fi Battles.
Unknown is not a legendary Pokemon but it is considered rare. Legendary Pokemon are one of a kinds.
no lileep is not a legendary pokemon but it is an ancient pokemon
Groudon, Kyogre, and Rayquaza. Groudon is the fire legendary pokemon, Kyogre is the water legendary pokemon, and Rayquaza is the air legendary pokemon.
Arcanine is not a legendary Pokemon because legendary Pokemon can't be breeded and arcanine can.
I can give my opinion on the strongest non legendary pokemon but that's all it'd be as each pokemon has a certain weakness (except magikarp of course) and so you can't truly say this is stronger than that pokemon.http://www.serebii.net/pokedex-dp/stat/all.shtmlAbove is a list of all the pokemon listed in order of their total base stats and according to that list, the non-legendary with the highest stats is slaking.
The legendary is palkia