On the Runescape Wiki there is a multitude of information. There are articles to read that give various information about the game. There are also news updates and announcements about upcoming contests and improvements. There is also a place to get questions answered.
A quest walkthrough for Demon Slayer can be found here: www.runescape.wikia.com/wiki/Demon Slayer
For help on quests, try using the RuneScape Wiki
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 below will redirect you to the RuneScape Wiki for a guide.
From my experience the rock crabs found in rellekka and drags if your a higher lvl Rune wiki has a good combat guide too
Several million players, apparently. Here are some details: http://runescape.wikia.com/wiki/Runescape
You could look through Runescape Wiki, search for it on Google. There is a guide on there for training skills efficiently.
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
It is against the RuneScape rules to give away accounts.