Concept

You're an orb. You're gliding (flowing? oozing?) around the world, minding your own business, when you see a glowy thing.
You decide to eat it.
You grow.
You keep on eating glowy things, until you feel yourself on the cusp of a revelation.
Now, you choose between teeth and ink.
With your newfound tools, you eat more glowy things, and find other orbs (are they other players too?) and keep on eating and changing
Eventually, you realize that you've become so big that now you have other orbs inside of you and you're producing your own glowy things!

Mechanics

Orb moves with mouse.
When you eat a glowy thing, you get bigger. At certain bigger-ness thresholds, you evolve. When you evolve, you are presented a pair of choices.
Running into players smaller than you (but not too much smaller. Spitballing to 10% of your mass or larger.), or biting players of a comparable size to you (or does biting let you eat chunks off of bigger players when careful?), eats them, which kills them and gives you an increase in size based off of how big they were.
When you progress to the third evolution, you're offered a choice between symbiote and parasite.
Symbiotes coordinate with each other, and are encouraged to work together.
Parasites are individually stronger, and seek out and consume symbiotes and other parasites.
If you're sufficiently small compared to another player, they cannot eat you in the first place and you can pass into their bodies and live inside them.
The inside of symbiotes is a peaceful environment filled with glowy-eaties.
The inside of parasites is an acidic hellscape bereft of any value save the malice dwelling within their hearts, and a small number of anemic glowy*eaties.