I had mirroring on both Euro & GamePotUSA and these are the changes that should be made to match it:-
1.) Mirror does have some AC/AMC on those servers. I don't know the exact figures, I would suggest this is based on a typical L40 Wiz AC/AMC
2.) Damage taken by mirror is equal to 1/5 that amount of MP only, not same amount. E.g. On Euro the guard would do 200 damage for example and my MP bar lost 40MP. This applies to all damage taken, you receive the 20% the damage amount from your MP bar.
3.) Mirroring does not take 18/37MP per shot, it takes MP overtime by reducing your 16-18 second regain. Level 0 reduced it somewhat, Level 1 quite significantly, level 2 made it so you hardly regained anything and level 3 made you lose MP per interval rather than regain it. So levelling it to L3 was a tricky decision
4.) Mirrorings damage increased with level, and this was visible from tests on the trainer. Level 3 did much more than Level 0 did and attacked significantly quicker. Level 0 had a delay which made it slower than a player while Level 3 matched the same speed. Overall levelling made it a huge different to damage output but cost you MP over time.
I did play ACE2M and I noticed mirroring was not the same as Euro in the above ways. The way it took mana per shot was a disaster and a mistake IMO, made it useless for PvE and was not as it was originally. As said it just become this useless PvP crap which I stopped using in favor of an extra pet.
Source: my memory, either everything I have said above is true or I have mental problems and remember fake things that I spent hundred of hours testing on trainer and making notes of in notepads.