Much data from http://dragonica.wikia.com/wiki/Score

A score is a numeral values received by players at the completion of a mission map. Scores are indicated visually on the score meter.

The score determines their rank, which influences the number of items received. There is also a "top ten" highscore list for each difficulty of an instance; getting a high enough score puts you on the list. This list is the only way to see your exact score.

Score may or may not affect experience received. No tests known.

Score calculation
Score is fairly straightforward to calculate:

Score = 80 + "combo" + "hit" - "hit loss" - "death loss"

With the four variables being the fields given in the mission summary.

Rank calculation
Score is converted into a letter rank, which determines the number of rewards.



Score details
The variables making up the score calculation can also be predicted. While largely an academic exercise, it can be used to estimate how careful you need to be during the boss fight.

Combo
Combo is the sum of all party members' combo score from the mission. It doesn't matter who does the combo, everyone benefits.

Combo points are awarded every 30 combo hits, up to 150 combo. More than 150 combo hits gives no more combo points, until the combo is broken and restarted.



Your personal combo points are listed in the in-mission number list, as "combo". Combo points are not awarded on the boss stage.

Hit
Hit is not entirely clear. It is believed to come from critical hits. A common value given is the number of critical hits done, divided by ten:

Hit = Criticals / 10

There is no entry for critical hits in the in-mission number list. It is unknown whether hit points are awarded on the boss map.

This may also be linked to the number of attacks done, as there is an entry for those in the in-mission number list. However, it is clearly not just attacks / 100, so if it is linked to attacks there is a more complex formula at work.

Hit Loss
Hit loss refers to hits taken. However, this is not just the number of hits. Each class has a different modifier.

Hit loss = Hits * class_mod

Known class_mods:

Thus, an acolyte taking 50 hits throughout the mission would only be penalized 40 score. An archer would suffer the full 50.

The raw number of hits taken is listed in the in-mission number list, as "hit". Hits are counted on the boss stage.

Death loss
Death loss concerns dying during the mission.

No details are currently known. There's likely a modifier on the death, meaning that each death would be gaining many negative points.



Notes:
* Time is not counted into the points system, unlike in alpha builds where time was a very important role.
* Attack Points are earned every time you deal damage, but do not impact the final score or rank.

TL;DR (Essentials):
* Get your combos up to 150, then stop them. Get as many 150 combos as possible.
* Avoid getting hit, but getting combos is a higher priority. If you need to get hit to keep up your combo, do so.
* Take as much time as you need.
* All combo points are shared among party members. That means that if you're an aco, focus on keeping the higher combo classes alive, etc.
* On the boss stage, don't bother keeping up combos, they don't aid your score.
* Getting hit during boss stage still lowers your score, so be careful.