After level 30 the difficulty of Neverwinter jumps up. However, unless you are rushing to end game, I don't think power leveling is really going to benefit you.
Mitigation in Neverwinter means exactly what the actual definition of the word means.
So for example, Ray of Enfeeblement has the following description:
Ray of Enfeeblement: Over several seconds, deal damage to your enemy while decreasing their damage and Mitigation. Debuff duration
increased based on stack of Arcane Mastery
SO, what this all means is for a period of time you've lowered the targets ability to reduce the damage from your incoming attacks.
Well how is the target mitigating (there's that word again) damage from your attacks in the first place? Good question, glad you asked.
Damage Resistance IS mitigation.
Damage Resistance decreases the amount of damage you take from incoming attacks. Defense helps to increase this stat.
Therefore, if you put this all together using what you just learned (stay with me now) it goes something like this...
"Target X" has a damage resistance stat 21.2%.
You cast Ray of Enfeeblement on Target X which reduces his damage mitigation by 15%.
Over the next several seconds, Target X's Damage Resistance (ie: mitigation) is effectively 6.2%
21.2% - 15% = 6.2%
Best Answer
Have your friend run though the areas you have access to. you will lose the XP for kills but completing quests is more important. So just have the powerful friend kill low level enemies and you focus on quest objectives.