Only posting this because I might have a few more details. I wasn't live streaming yesterday, but mid playing plain dangerous. Sand bari was dead, I'm sure anyone who has done this quest also knows that diablos then jumps out of the group in 8.
Ever since this glitch came out I have attempted to hit a monster as it came out of the ground. For weeks nothing. I was using poison ds, (so no slime), I start swinging diablos pops up out of the ground horn busts off. I pretty much knew what was going on and was just mad I didn't have any film running. Sure enough Diablos continues it's animation.......pretends like it's a fresh diablos. I got hit from it jumping out of the ground.....so I put my weapon away ran back toward it. Dead 1 hit.
The other 2 group members as well as myself did not have Weakener.
Summary - Diablos came out with both horns, not pre injured, seemed to take a massive hit from my blade during the "initial monster spawn", the horn busted off as it was still jumping into the air with no stall as it continued the standard come out of ground and grumble like it's going to rage that it does when it first spawns. Obviously diablos comes out of the ground HORN first, and this time it appears I managed to hit the "exact location that pops out of the ground first immediately as it spawns." It also registered a hit on me so obviously you cannot STOP the initial monster spawn "cutscene". I'm not going to speculate any farther than this, but hopefully this helps someone figure out this weird glitch.
"But wait, why would you be swinging there?"
Myself and dozens of friends have been trying to do this since the first reports come out and have never been able to replicate it until now. We pretty much stand on the spawn locations where monsters dig out of the ground swinging every time just in case it were to happen. This is why I was swinging. I can't believe it finally happened and that I wasn't streaming.