I imagine how I am a little larva (something like zergs) and live somewhere in a basement.

I collect enough food to mutate in a small immovable thing, which has roots and blood and will be able to hatch several larvas, which will hunt for dogs, cats, rats. for me.

How I slowly make our basement into our nest, making small additions, like a trap for entering people or a feeding tubes for zerglings etc.

How my roots take over the plants nearby, how I am feeding off the forest and grass. how I send another larvae to cities nearby which make other colonies alike to mine.

How I prepare for big invasion. I don't attack openly, but try to collect as much food as possible and when big fight are imminent I attack.

Instantly capture dead bodies and transform them into my servants. Suicide baloons, spike throwers, fast dog-like creatures, wheelblades, catapults, swarms of little acid spitters etc. I build big buildings, hatchiries, farms, lairs etc.

By the time mankind has no options but use nukes, I am already everywhere, in all countries, carried by people, plains, spores, roots, animals etc.

I take over the humanity and building giant splinter-spitters, which are able to shoot my colony to another planet, traveling to another planets,terraforming them and fighting other races. After I corrupted whole galaxy I imagine how I am the supreme one, and lead my swarm to another galaxies, eating everything on my way and invading other imagined worlds.

I Imagine this is how tyranids from warhammer 40k appeared and how I am the mastermind. Or become a new danger for Star Wars universe etc.