IBom "other" damage

I tried searching for this first but didnt see anything relevant. I was fighting Immortal Abom mini boss in AQ with like 85-90% health and then suddenly just keeled over and was KOd. As you can see, I was using Omega Sentinel, who is poison immune and usually wrecks Abom. So what was this 30k of "other" damage that suddenly killed me?

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If you accidentally stack 10 poisons on you, you're done