Antagonist idea:Brainbug

[Asparaguy]

A rough idea of mine harkening back to the ideas of cortical borers and sentient diseases of other servers. You are a brain bug, a microscopic alien infecting a singular crewmate, you spawn in one. The first thing you notice is that you are not in the station, you are in a custom z-level representing the body. You will be able to walk around inside the body and interact with certain things, such as interacting with the eyes and looking through the crewmember you are in. Your main goal is to increase your 'spread'. You can do this by interacting with an 'evo pool', a pile of slime in the right part of the body z-level. From There you will be able to access a sort of tech tree, using spread to buy upgrades. There are three main paths you can go through in the upgrade tree, Symbiosis, Neutral, and consuming. The Consuming path involves buying upgrades that lower your hosts health, increasing your spread but causing them to go against you via the ingestion of antibiotics (upgrades can reduce the harm these do however). The symbiosis path takes longer, as the upgrades give you less spread, but give your host helpful upgrades such as increased stamina, or healing chemicals. The neutral path involves buying a combination of both paths, so its the most commonly done. Each path has their own end game,
The Neutral path ends with you hatching a player controlled larva that will wriggle its way out of the host's ear, it will look for a new host, and the cycle will complete.
The symbiosis path ends with you becoming one with your host, allowing for incredible powers such as the ability to breath anyway, resistance against damage, and the ability to come back from the dead
The consuming path ends with you taking over your hosts body, replacing their limbs with yours, and taking over their brain, killing then. You become a rampaging monster, shambling abomination esc. (Note, it is okay if you die in this state, you already won if you take over the body)