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No, it's not very effective. I recommend ice type.
Any Dragon-type really. But it must be in it's final evolution. Ex. Dragonite Garchomp
The dragon scale is located in Mt. Mortar
The move deleter in Pokèmon HeartGold and SoulSilver in in Blackthorn City. He is in the building with the sign outside, and on the inside, it is the place where the old lady teaches your Dragon-Type Pokèmon the "Ultimate Dragon-type move" (Draco Meteor)
Go the Blackthorn City and Fight the 8th Gym Leader who uses Dragon types so bring strong Ice or Dragon Type Pokemon.
It would be best if you use Ice-type pokemon, because the blackthorn gym leader has dragon-types, and ice-types are super effective against them. Dragon type moves are also super effective, but if your going to use dragon type moves, you should use NON dragon-type pokemon, only dragon type moves. Because they could probably faint you easily if you do, because, dragon-type moves are super effective on dragon-type Pokemon.
Well the last gym leader is a dragon type leader so you need an ice type pokemon and/or dragon type pokemon. Idk what his name is but a guy gives you a level 15 Datrini and it is a dragon type pokemon. For an ice type pokemon, go back to the cave (idk the name of the cave but it is a ice cave) and get an ice type pokemon like swinub and raise him and beat Blair!
Her Pokemon types are just plain old dragon types. She also has a Kingdra, and I think 2 Dragonairs, from what I remember in SoulSilver.
I know every now and then you can get it at the pokeathlon. Sometimes dragon Pokemon will be holding them when you catch them. Hope I helped!
at indigo plauto
The dragon's den in Blackthorn city
you get it after catching or defeating red gyarados