Nitrodon and I have crashed Earthbound while making the TAS. I've put up some SMVs demonstrating the crashes on my webpage. They're named "Z-Bug1.smv" and "Z-Bug2.smv". You can get them both here:
http://www.obellemare.com/speedruns/
The game simply freezes. You can't do anything anymore. It's basically a buffer overflow somewhere in the game's memory (Too many sprites loaded at the same time without cleaning the memory of the obsolete spirtes (those not on screen anymore)).
The first video is a bit short... but I'm too lazy to go back and re-record it to be longer. Basically, we teleported through the lost underworld and this is what happened at one point. The second video happened at the end of the game. Paula prays to get help from people. This scene was the runaway five praying, but it just never loads. The game doesn't have enough memory available to load all sprites, so it gets stuck in a loop.
I know, it's not a Tool-Assisted-Crash-Speedrun (TACS), it's just a crash in the game... I might or might not try to find a way to crash it sooner. Until then, these 2 videos will have to do.