During the early days of colonization, the player’s first task is to begin to explore the strange alien landscape upon which his faction has found themselves. It’s inherent in the genre: the first ‘X’ in 4X stands for eXplore, after all. Anyhow, when he does so, his units will inevitably happen upon a strange alien icon that looks like a collection of squiggles. It promptly seeks to kill his units and damage his bases.
This unit is called a mind worm boil. And they are what serve the gameplay role of the barbarians in previous Civilization games. These units spawn from fungus squares, either randomly or as a response to an exploration unit attempting to traverse the fungus, and they are hostile to all the human factions on Planet. Essentially, in the early game they are intended to force the player to build early military so that he can’t just expand in peace until he encounters another faction.
There are a few strange things about mind worm boils that become readily apparent to the player. Unlike human-to-human combat, mind worm boils do not have unit strength. Nor is the player’s unit strength used in the combat calculation. Against mind worms, it doesn’t matter at all what weapons you use or what armor your troops are using. The only things that matter are whether you are on the attack or defense, whether you are defending in a base, if there is a sensor array around, and most crucially, the experience level of the troops.
But then, the first time a mind worm boil attacks the player’s settlement, the game breaks away into a small short story. The content of the story is the same whether the attack is repelled or if the base takes damage. It describes just exactly how these mind worms kill people, along with the aftermath of the battle on the base. It’s chilling stuff.
See, it turns out that the mind worm boil is psychic. As it approaches, it radiates waves of madness and fear. Then once the defenders are insane, paralyzed, or catatonic, the worms swarm over the people and lay their eggs in the victims’ brains. To make it even worse, the worms themselves are small and they can tunnel through solid metal. So fixed perimeter defenses don’t help you. You can’t hide behind the walls. When the worms come, you have to fight them or die screaming.
This is why weapons are irrelevant and why morale is everything in psi combat. Battle-hardened, experienced troops can resist the mind worms’ effect. And if the wielders aren’t driven mad, all it takes is a couple of flamethrowers to burn out the boil. That’s well within the technical capacity of every faction from the start of the game.
This is also why troops get a major advantage in psi combat when they’re on the attack. Which is a really insightful mechanic to add into the game. After all, it is true that people are naturally much more psychologically stable on the offensive. Being able to pick the time the engagement happens and having the luxury to go in with a plan helps a lot.
The other thing that’s worth mentioning is that these mind worm boils can be co-opted by human factions that have a positive Planet score. Since the Gaians start with a +1, that means that they can capture mind worms from the beginning of the game to turn on their enemies. On the one hand, that’s a cool bonus. Early mind worms make for excellent exploration units and can make you a bunch of money.
On the other hand, it’s freaking terrifying. Just imagine what’s going on there in detail. The Gaians are sending crazy witches into these writhing worm piles to travel with them and convince them to eat the brains of their rivals.
This knowledge makes the Gaians’ religion much more hardcore. The mind worms are the dominant form of animal life on Planet. So when the Gaians worship their new home, they are in large part worshiping the worms that visit death and terror on mankind. This is much less akin to silly crystal-wielding New Age mystics and much more like the old blood sacrifice paganism.