This morning I played Great Mothers with Morgan and NS Spirit vs. Omega (Fugitive) and I believe it was Wrecker and Hunter Mercenary in GAC 3v3.
I doomed Wrecker first. I dealt damage until his health was reduced to 0, he went captive for a few turn and then died.
Next I doomed Omega (Fugitive), but it seemed that I was not able to deal any damage to her. So, I went for Hunter Mercenary. I dealt damage to him until his health was reduced to 0, he went captive for a few turn and then died.
I focused back on Omega (Fugitive). There were damage numbers appearing next to her character, but she would not take any damage. Eventually, her health got reduced to what looked like 1 point, but still no damage was getting through to her. I timed out as she was unkillable.
Here is a screenshot of it:
