I had the idea for trying to unravel the mysteries of challenge score for several months. While I do not have a lot of answers, I did find out a few things. More answers will come after I am able to run a lot more tests. I saw that @alcaselzer posted something 3 days ago but I didn’t even see it until now…he or she is welcome to use my data.
Before I start, none of this is set in stone; I may have made errors in my observations. In addition, SG changes scoring in the challenges so exact formulas may break down over time. However, the concepts will endure.
I based my data on stage one of Rare (Beginner) but I did see the scores of some of the other stages. I am breaking this information up into three posts.
The enemy score total is not quite the sum of the monster hit points but is in the ballpark. It turns out that the health score is 80% of the enemy score. For the Rare stages, they are as follows (note that I only filled in what I observed; the others are easy to fill in):
Stage____Enemy Score__Health Score__Stage Multiplier
The intermediate and advanced are 1.5x and 2x the rare stage. I have informally looked at monster hit points before and I assume the other stages are the same but I did not verify this.
Stage____________Enemy Score__Health Score__Challenge Multiplier
Rare Stage 1________5500_______4400_________1.0
Epic Stage 1.________8250_______6600_________1.5
Legendary Stage 1.__11000_______8800_________2.0
The method for calculating these parts of the score is straightforward. The enemy score is like a constant, you get it for beating the stage. The health score is the fraction of your total hit points on your team and multiplies it by the perfect health score. For example, if your heroes all have 1000 hit points, and two are dead and three healed, your fraction of team points is 3000/5000. Let’s suppose you are on epic stage 3. The formula would be:
Your Health Score = Ideal Health Score of Rare Stage 1 x Fraction of Team Hit Points x Stage Multiplier x Challenge Level Multiplier
4400 x (1500/2500) x 1.24 x 1.5 = 4910 of a possible 8184 for the stage
I have not tested this extensively so there may be a small discrepancy for rounding and other factors. I do not think there is a penalty for dying although there is a continue penalty that I did not include in this analysis.