This is a follow-up to last week's D&D.Sci scenario: if you intend to play that, and haven't done so yet, you should do so now before spoiling yourself.
RULESET
Code is available here for those who are interested.
CHARACTER STATS
A character has two stats: an Element and a Power Level.
18 of the 19 characters are power levels 1-6 of the elements Fire, Water and Earth:
The remaining character, the Nullifying Nightmare, has a Power Level of 5 with the unique element of Void.
The NPC team consists of Fire 5, Water 6, Earth 3, Earth 4, Earth 6.
Congratulations here to abstractapplic, who was the first to figure out the elements.
HOW CHARACTERS FIGHT
A fight between two teams is composed of fights between the individual characters. When two characters fight one another, it works as follows:
Some elements counter others:
Fire is countered by Water
Water is countered by Earth
Earth is countered by Fire
If one character's element is countered by the other, that character loses the fight (regardless of power level). For example, if Oil Ooze (Fire 2) fights Greenery Giant (Earth 6), Oil Ooze will win.
If the characters are the same element, the higher-power one will win. For example, if Phoenix Paladin (Fire 5) fights Fire Fox (Fire 3), Phoenix Paladin will win.
If the characters are the same element and the same power, each has a 50% chance to win.
There are two special cases:
The 1 of each element counters the 6 of the same element, and beats it rather than losing to it. So if Volcano Villain (Fire 1) fights Blaze Boy (Fire 6), Volcano Villain will win. (Congratulations to Yonge, who I think is the first person to have explicitly noticed one of these counters).
The Nullifying Nightmare has Power Level 5, and the unique element of Void. Void does not counter any elements, and is not countered by any elements - the Nightmare just fights with Power Level directly, as if it were the same element as its opponent. So it will lose a fight to any Power 6, have a 50% chance against any Power 5, and beat any Power 1-4.
HOW TEAMS FIGHT
To find the outcome of a game between two teams:
Choose a random character from each team.
Those two characters fight.
The loser is KOd and removed from their team.
The winner sticks around.
Repeat this process until one team has run out of characters. That team loses.
This ruleset encourages balanced teams. For example, a team of 5 Fire characters will lose to a team of 4 Earth and 1 Water characters. Even though 4/5 of character matchups favor the Fire characters, nothing on their team can beat the one Water character, and eventually it will work its way through their whole team and win.
Once you understand how the rules work, general strategy is:
Choose high-Power characters.
Try to be reasonably balanced elementally.
Try to counter the enemy team (with 1s against their 6s, a tilt towards the right elements, etc).
The elemental counter mechanic does not always work as you might expect it to at the team level - rather than thinking about countering your opponent's common elements, you should think of it as targeting your opponent's weak elements. If your opponent has 3 Earth and 2 Water characters, for example, rather than saying 'that team has lots of Earth characters, I should bring high-power Fire characters to beat them' (which will get you wiped out by the Water characters), you want to say 'that team has no Fire characters, I should bring high-power Earth characters it won't be able to beat'.
DATASET GENERATION
The games you have access to were played by players grouped together by the games auto-party functionality. These players do not build coordinated teams, so there's no correlation between characters.
However, some characters are more popular than others (most notably the Siren Sorceress, whose infamous costume has won her a large and...enthusiastic...fan base).
Overall, Water characters are somewhat more common and Earth characters somewhat less common. This doesn't affect the game itself, but it...