Make sure to try this on a fresh profile unless you’re fine with messing up your stats.
Essentially, by having two Mr. Bones active and losing by emptying your deck, you’re stuck in a loop of both jokers triggering, somehow advancing into way higher antes (I think 3-digit is supposed to happen, it only went to 50ish or 70ish when I tried it tho).
There should be videos that explain it better. Just thought I’d share with you guys in case someone didn’t know this glitch :)
I think this is called the Sans Undertale skip. I saw some videos a while back of people getting to ante 300+ lol. It also seemed useful for the any% speedrun.