[Finalgenesis]

communion gives boost to master as follows:
2 slaves = +1 path
4 slaves = +2 path
8 slaves = +3 path
...etc

Mind burn is a S2 attack, every 2 extra level gives it +1 Penetration. So if you are using a S4 mage, you already have +1 pen, using 4 slaves is sufficent for another +1, the next step up is 16 slaves (you might as well put void eye + magic focus rather then adding 12 more slaves). Your mind burn will have a MR check of 14 (base 12 + 2 pen), lets say this thug has 20 MR, you'll only roughly have 11% chance to beat the MR (refer to manual for the chance table)