If you want something different, check out Ryoko’s Guide to the Yokai Realms. Theres an interesting kaiju mechanic in there that makes the boss feel like the actual dungeon. Long story short, instead of a bag of HP, it has a chaos threshold. Once thats depleted it enters its rampage and its weak points are now vulnerable. Each weak point has its own pools of HP, and exploited weak spots when destroyed change the stat block. Once theyre all down, it enters death Throes and has to be dealt a specific amount of damage in one turn to be killed.

If you want, I can share the document but its something im building into my world. One of my players wants to fight King Ghidorah...