This is just a quick overview.
Methisgood is Jagex impersonator. His usual method is to lurk in the Grand Exchange looking for a player. The level variety is very wide with me being Combat level 62 at the time. When targeting a player he will add them then run out to somewhere, maybe Barbarian Village. He will send a message saying that he is from Jagex and can make you a member for 1 year free of charge. If you agree, he will ask for your pass backwards. If you decline he will say that he will ban you. Do not be frightened by this and just report him for Jagex impersonation. He has a sense of humor by ending his message with "goodday".