The Hydra That Wouldn't Split

The Abyssal Tide has a legendary hydra that is supposed to split. For a long time, ours only came back to life once, and that was it.

The problem wasn't the hydra. It was bigger: the game only knew 17 kinds of effect, and every more exotic ability got squeezed into the closest one. The hydra became a resurrection. Curses meant for a single target became weaker auras. Fourteen factions existed on paper, with buildings, troops, costs and upgrades, but many of them still didn't play the way they should.

The fourteen

Fourteen factions is a lot for a two-person team. Each one needs its own way to win:

• Crown: knights, marksmen and mages, with blessings and holy resurrection.
• Bone Legion: zombies, necromancers who raise skeletons and vampires who turn their victims.
• Steppe Horde: brutal infantry, shamans who strengthen the troops, war beasts and totems.
• Sun Court: agile archers, precise swordsmen and solar magic.
• Moon Sentinels: multi-target arrows, binding roots, assassins and specters.
• Ancient Grove: poisons, healing, bears that stun and stone giants.
• Northern Clans: swift wolves, frost spearmaidens, trolls that freeze and the endless winter.
• League of Gears: tanks, flamethrowers, automatons and energy shields.
• Abyssal Tide: regenerating scaleborn, bouncing serpents and the hydra that splits.
• The Corrupted: cursed trees, void creatures and infernal engines.
• Abyssal Pact: demons, volcanoes and spells that wipe out whole armies.
• Kingdom of Sands: quillbacks, vultures, brutes, sand mages and storms.
• Elemental Conclave: spirits of wind, water, fire, lightning and earth.
• Jade Empire: healing monks, hard-to-hurt drunken brawlers and celestial chi.

An ability is a sentence

The way out was to stop writing each ability as a special case. In the new engine, every ability is data with three parts, almost a sentence: when it happens, on whom and what.

The "when" can be when attacking, when struck, on a kill, on death, when mana and cooldown allow, or when you press a button. The "on whom" can be the nearest enemy, the most wounded ally, the largest group, a line, a cone. And the "what" is the effect.

A Bone Legion vampire, for example, reads like this: on kill, take the victim and make it an ally.

With that, each faction got its complete set: spells with mana and cooldowns, lasting curses, frozen buildings, sheep, banishment, invisibility, summons, mind control, resurrection, mines and storms on the ground. The hydra finally splits. And the Bone Legion was rebuilt from scratch, with zombies in three tiers and vampires that grow into Vampire Lords.

A reality check

Then we ran the first round of AI-versus-AI matches with the new abilities.

Win rates ranged from 10% for the Abyssal Tide to 86% for the Jade Empire.

As in chapter 4, we tested cause by cause before touching any number. Taking the Healing Spray away from the monks dropped Jade from 87% to 40%. Taking the shamans' blessings away dropped the Horde from 71% to 35%. Two abilities were carrying two entire factions.

But part of the blame was the AI's own. Playing the Abyssal Tide, it poured gold into the faction's weakest building line. Playing the League of Gears, it built several Power Plants, whose auras don't stack, and far more Hangars than the anti-air defense called for.

So the AI learned three things: one Power Plant is enough, anti-air should match how many flyers the enemy really has, and each troop building gets a weight from measured win rates. Whatever imbalance was left, we evened out by making each faction's AI train a little faster or slower.

In the final round, the gap between factions was smaller than the measurement's own noise.

What that number doesn't prove

Two caveats, because they matter.

The first: the training speed adjustment applies only to AI teams. You always play with the faction's real numbers, the ones in the tooltips, against the AI and online.

The second: this balances the AI, not people. How Jade Empire fares against Abyssal Tide between two real players hasn't been measured by any simulation yet. That answer only comes when people play. In the meantime, you can get to know all fourteen on the factions page.

While Castle Arena was learning to balance itself, another game began to take shape at the same bench.

— The team