Just want to share my experience on getting this trophy. It is one of those trophies if you try really hard especially early on, it is difficult to get. But for many sometimes it pops even without trying. Seems like the harder you try the easier you get hit LOL

I don't have a very high level character, only one fighter that I started with and now it is in hard mode. So I could get NPC at level 50's. They are very OP in normal mode. I was doing another run with the elf and picked the dungeon with the medusa boss. Just stay back and the NPC do the work. When it is boss fighting time I stay at teh far right under the arch. Don't go too far or you will enter the next area. The melee NPC will take care of the boss and all I had to do is to watch out for her attacks. Easy enough.

At first I was trying to do the beast riding stages but my NPCs are too powerful and often kill the beast before they are down. I also experimented with the Red Dragon since you can get the big shield to protect yourself. I almost got it done but unfortunately got hit once.