The Mentor is the main adviser to the Learner when it comes to playing the game, helping him/her succeed in the challenges that the game throws at them.
S/he is a supportive, elder sibling figure, whose apparent age is about two years older than the learner.
The Mentor is strictly there to advise and suggest, not to tell the Learner exactly what to do - the object, after all, is for the Learner to develop his/her own thinking skills not just blindly follow.
If the Learner does something that the Mentor has advised against, the Mentor will sit to one side, cheering the Learner on from the sidelines, and if it has all ended in tears, he’ll pick up the pieces.
S/he might also share some of his/her previous adventures as examples of how certain techniques can be used to good effect. Or, how they went wrong, because s/he didn't think it through first!