I pulled off a +296 modifier the other day.
I was the Dragon Rider. Due to a glitch in the Digital Edition I couldn't get through the Portal of Power. (No, I didn't have a Warlock Quest.) I had to keep running around until I could change the terrain on the Portal.
In my running around I collected 37 dragon scales. I also had the Dragon Amulet (all scales match your opponent) and the Dragon Talon (all scales add 2). I then encountered four enemies on a single space in the Dragon Tower. 37 * 2 * 4 = 296