Field placement is crucial in a MN file. I lost matches I should have won just because I screwed up on troop positioning. That gun guy needs to be front row and I find optimal placement to be Gun, Commander, Greg on center row.
If you're using revival SS, I learned that units are not ranked up upon revival and lost a match because I didn't know that.
It's important not too over-commit on the amount of units you bring out. I often have enough SP to keep pumping out units, but this leads to SP lock troubles. I would say that once you have 4 units out, stop. Adding another unit will probably not help that much and has the potentional to hurt you.
It's nice to have a free revivor, but considering the order of unit summons, she does not come out until mid-late game where SP is less important. I still would keep her in the file for those matches where you can't keep doing the same thing and expect to win.
The rank-up open skill mercenary unit is awesome, but he often works against Greg's focus skill by leveling up your units. On the plus side, you get some return protection. Anyway, adding this guy was probably the best thing that happened to my file.
Abuser Punisher / Callonia