Dragon-type Pokémon are weak to Dragon, Ice and Fairy-type attacks.
They are pretty much resistant to anything else. If they aren't, their high Defense and Special Defense will usually make up for it. The only Dragon type attack that does not deal double damage to other Dragons is Dragon Rage (always hits with 40 HP).
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A dragon type's weakness is, believe it or not, is dragon type.
Ice and Dragon type moves.
It's only proper weakness is dragon type moves
Ice, Fairy and Dragon-type moves. You have to consider their secondary typing, though.
Haxorus is only Dragon type, and as with all Dragon type Pokemon it's weaknesses are Ice and Dragon. I would recommend not using a Dragon type Pokemon though because you leave yourself open to high damage from Haxorus' own dragon type attacks.