I have posted a link below, that should have the information that you require.
Chat with our AI personalities
Wiki Answers will not provide the information to break the rules of RuneScape.
every monster has a weakness, it depends which dragon search it up in runescape wiki
go on runescape wiki
The following link will redirect you to the RuneScape Wiki for a walkthrough.
There combat level is usually 122 or 127 link to wiki hellhound: http://runescape.wikia.com/wiki/Hellhound