At any time, go to Rook and ask him which monsters are a challenge for you. Say Monster_Name. He will respond with a clue as to how difficult the monster is to you, and if it may help hone your skills. Examples of his tips are as follows:

1) The Monster_Name would hardly be a challenge for one such as you. It wouldn't be worth your time to hunt such an unworthy opponent.
2) The Monster_Name would be a fair fight for you. You might even pick up a new trick or two.
3) The Monster_Name is tougher than you imagine, but will surely help you hone your skills... should you survive.
4) The Monster_Name is a fearsome foe. Attacking would be tantamount to suicide.
5) The Monster_Name is a fearsome foe. Attacking would be tantamount to suicide. Probably best to tackle with friends beside you.