Never seen anything personally offline, but when I was younger and dumber I went searching for real snuff online at one point.

I'll sound some stuff that was absolutely horrifying. You can find similar stuff today by simply searching for cartel execution videos and such, but it's hard to find stuff of any real definition. But there are the few odd ones out there with high quality video and audio.

One I found was a young woman somewhere in south america being set on fire and writhing in the mud screaming as she slowly burned alive.

Another I found was some young asian-american woman having her stomach slit open and her intestines cut out while she screamed and vomited. This one really got to me because she was begging well after she had been entirely disemboweled.

Last one I can think of off hand was a woman who had her face cut off, but she was nearly dead already when they did it because they had beaten the shit out of her. I'm not sure she was even conscious at that point, maybe even dead already.

All of them were horrible, 0/10 do not recommend. Keep it to fantasy. Consensual stuff can be fine if everyone involved is on the same page but keep in mind it's dangerous and make sure your partner understands the risks. Many people have died during auto-erotic asphyxiation attempts.