The Transmogrifier! (You can download it as an actual Excel file, rather than as a Google document.)
What does The Transmogrifier do? Well, I’ve been working on a long article about the mechanical challenges of epic tier play and I realized that it might be helpful to give GMs a tool to tune their monsters. What the sheet does is show you numbers that are balanced for the party, allowing you to adjust for your table’s specific level of optimization. Please read the notes within the spreadsheet, they explain aspects of the tool.
Why doesn’t it use averages instead of the high and low values?
Because the high and low values are the problem children, they’re always going to stick out. If one character has much higher defenses, it’s that quality that needs consideration.
That “How difficult is your game?” thing is confusing. What do you mean?
Your party is a spectrum. Let’s say that the high/low AC are 20 and 10, with the difficulty set at 60%. This means that the calculations treat the whole party as having a 16 AC. By increasing the difficulty, you’re saying that hitting the characters at the top end of the scale is more important than missing the characters at the low end. This will change the play and development of characters on the low end, as they will seek ways to cover this deficiency. Setting the value low increases the impact of optimization. In this example, if the monsters are tuned to hit a 14 AC, the character with the 20 AC will be relatively immune to them.
Why does it only consider monsters of the party’s level?
The level box is there to give you the normal values as a point of comparison. If you want, you can “cheat” by adjusting the level without changing the party stats. This will give you a snapshot of how challenging the monster would be by contrast to the party.
Five hits to drop?
Actually, the system math appears to be based on 100% hit, 4 hits to drop. My method simply includes hit ratio.