I've had the effect trigger after getting hit for 2 damage in a round. Never had it trigger with 1 damage. Higher damages always gave the effect.
I got 2 energy of the effect while in combat somehow, but then of course when combat ends, it decrements it to 1.
So, I'm working on trying to draw out the secrets of the various ooze items, and I think this is the only one I've got a handle on so far. After a while experimenting, it seems to pretty reliably be the case that I get one energy of Ooze Symbiosis when I use an evasion technique and successfully block all damage from the incoming attack.
Doing the same again during the same fight doesn't add another energy of the effect, although I could swear I've at least once had 1 energy remaining after a fight. But that was before I noticed the link with evasion.
I'm getting three turns of symbiosis now, which goes down to 2 unless I manage to run away for free. Not sure why it's different - I have been feeding it a lot of items this run, or perhaps Kinak changed it to make it easier somehow.
So before I fed my ooze hundreds of things, I was getting 1-2 turns of ooze symbiosis (before ending the combat). Now I'm getting 2-3 turns of it. I wonder if it's from feeding a bunch of stuff, or more specifically from feeding it stuff that gives the bizarre combinations.
(Or just bad/good luck)
Nothing too fancy, probably smelly old pants (that's my usual go to junk pants), though I had fed it literally every other kind of pants to it earlier that day.