Concerning the battle tactics of the Biomass
From records pulled from citizen journals and narrative drones, we can evaluate the tactics that the Biomass uses. Perhaps it is not accurate to use the word "tactic," as if the Biomass had some sort of strategic intention. It is, after all, a contagion and not an organized enemy. However, we do use the word tactic in biology to describe the action of microbes and even biochemical pathways.
The biomass is thought to have evolved methods of invasion on its home planet in the 13th solar system discovered by the Pathrons to have one yellow medium star orbited by 8 planets, that is, YM1-8-13. It is the opposite of the typical invasion technique used by so many warrior species that involves attack with heavy weapons, then medium-weight weapons, and finally infantry with light weapons.
The idea of this strategy, which I will call the standard progression, is to destroy the target's large defenses, then small defenses, and finally root out any survivors. This allows destruction of an enemy before they have time to bolster themselves and fight back.
A common example is the Phrug invasion on Yaxosphere in the first interplanetary war. The Phrugs would attack a city from space, with heavy orbital weaponry, then from the ground in armored vehicles. After a city was already hopeless, foot soldiers would come in and occupy the Yax city.
This worked for the Phrugs as they had limited resources. It was difficult at that time to transport weapons from Phrugosphere to Yaxosphere. The orbital weapons could deal a significant amount of damage without themselves being damaged. Then the armored vehicles could crush any additional resistance with little damage to themselves. By the time the unarmored, more vulnerable foot soldiers arrived, there was no resistance. Thus the Phrugs conserved a finite number of troops while still taking territory.
The Biomass is not limited in the same way. It has no compassion for the life of the infected, so if it sends in a thousand runners to their death, there is no loss. In fact, runners do not appear to have much longevity as it is; they will die within a few hundred time units with or without being damaged by a drone. For that reason, when it invades, it sends in runners as a first line of attack. They are easily killed and do little damage to the infrastructure. Were this a normal army, the attack would be useless.
While they do not damage infrastructure, they certainly strain it. Even their dead bodies act as warriors for the Biomass army, because they decompose and spread infected cells about the invaded area. Any injuries they cause, however slight, kills their enemy and recruits more soldiers.
The apes generally come next. It takes the Biomass infection more time to convert a person into an ape than it would to convert a person to a runner. The Biomass therefore has an incentive to preserve them. The apes therefore have a sense of self-preservation. These stronger, more intelligent creatures herald in another army of runners. They have better success against the strained target city. They only need to cause strain and hold territory, because the smaller forms of the invaders, the bacteria and the viruses, attack the occupants as longs as medical and military intervention are withstood.
The more significant attackers, the "freaks," come only late in the invasion. Sometimes they are giants, sometimes they are unusually intelligent, sometimes they are venomous, sometimes they are impossibly fast. They destroy what is left of the city, reducing it to rubble as the Biomass turns all uninfected organisms into infected organisms.
This process is essentially a reversal of standard progression, so I will call it reversed progression. Standard progression works for most military groups because they must transport all of there resources from a distant home to the infected territory. Reversed progression works for the Biomass because the infected territory becomes a resource, even before the invasion is complete.
Aside from this, the Biomass is limited in tactical ability. The runners simply run at any uninfected person, bite, and flail their arms. They will not kill a person, but the venom on their claws and teeth will knock a person unconscious until they also become a walker, or something worse. The apes know to hide from attackers, to surprise, to flank, and to team up. They cannot perform any more sophisticated tactical maneuvers. The freaks are impossible to classify. Sometimes, as in the beginnings of the infection on Kkruk, they are quite capable of espionage and sabotage. Sometimes they make walkers look intelligent.