Unfortunately, the Roxy/Poison bug I have no idea how to make it happen.
Holly Wood/El Gado/Rolento Immortal Bug, how to activate and deactivate ithttps://gofile.io/?c=IIamD3
As you can see, Cody grabbed Holly Wood and Guy hit him with AB, even though he had 1 HP, he can have more than that, the secret is that the AB needs to kill him when you friend is holding him.
When Cody died the first time and respawned, Guy went to a hit that wasn't a grab, so Holly Wood kept immortal, but at that point, Guy or Cody could have grabbed him and killed him, the key to deactivate that bug is the respawn itself, it allows you to grab the immortal enemy once, but only if you don't hit him with any other attack. Since Guy hit him with a flying kick, so now you can't grab him anymore, so you can't kill him and need to die again.
After that, Cody died and respawned again, giving another chance to go straight to the grab, this time guy goes to a grab and finishes the immortal enemy. If guy hadn't grabbed him, instead he had hit him again with any other attack, the enemy would have kept immortal and another death would be needed.
That bug works identical to Holly Wood, El Gado and Rolento. It is more common to happen against Rolento because when he is dying he starts to throw grenades and the best strategies are to grab him or hit him with AB, and if you are playing with a friend, if one goes to the grab strategy and the other to the AB strategy, well, that's exactly how to activate it. I have seen it happening lots of time against any of these 3 playing online.