Is a runescape power leveling illelgal?

Answer 1

"Power leveling" as offered by companies - you pay them to level up your account - is against the rules, and very risky. It is against the rules because the rules to which you agreed include not to share the account with anybody, and not to pay any real-world money to get advantages in the game. And it is risky because you need to give somebody else your game login and password.

"Power leveling" may also refer to any technique to quickly level up some skill. For example, dropping minerals that you mine (such as iron) instead of taking them to the bank is known as "drop-mining", but also as "power mining". There is nothing against the rules in this; it is really your choice whether you want to forfeit the money (from selling the minerals) to get experience faster. Similarly, other tips and tricks as explained in online guides such as runescape.wikia.com are acceptable.