Probably the patch you're using isn't compatible with the bosses and because of that, it won't load correctly and then the ROM freezes.
Also, be careful about freespace, this could be the problem, the freespace you're using are corrupting important data and this could be the reason of the crash.
*Being with Toriel fills me with Determination!*
Super FX is a really underrated chip.
Don't ask for ASM requests. Request your ASM elsewhere.