In your opinion, what are the essential tools for mentoring services for young offenders?

Hope it will be helpful.

I appreciate your quick and helpful answer.

This is an interesting and important question, although the specific context that you wish to apply is not certain. Regardless, some critical qualities, in my view and supported by research, include:
• Accepting and non-judgmental
• Warm and empathic
• Able to relate to the youth's personal circumstances and environment
• Strong pro-social role model, but not excessive or 'over the top.'