Although this is super creepy, this boss battle would have been incredibly interesting had it made it into the final product.

"The premise of EarthBound 64 was going to be much, much darker."

4:16 When you think better

I always imagined this fight as witnessing Claus losing himself to his power.  Throughout the battle, you actually witness Claus' body being torn apart and ending up the form of Vapor 2; much like how we saw Giygas in Mother 2.  I'd like to think of it as Claus becoming a psycho kinetic wraith, like Giygas.  

this isnt scary at a- "aeolias table suddenly attacked" oooohhhh thats unerving. "vapor 2 suddenly attacked" nope nopenope noooope soooo much nope.

No wonder Lucas is so scared all the time.

No wonder they called this mother cause people keep saying MOTHER OF GOD WTF is that my reaction to second to last phase

Looks like Lucas ate the mushrooms again.

Phase One: Claus's fate is unknown.

"Aeolia's table suddenly attacked"

Sign Suddenly Attacks

"You encountered Dung Beetle!"

Itoi was a master at creating fights that were genuinely terrifying without the need to resort to over the top imagery or sound.

This is like creepypasta that's actually real.

Dont you hate it when you get attacked by a straw?

"Vapor 2 suddenly attacked!""

According to Itoi, the island where you trip out on mushrooms had to be toned down a bit. This psychedelic sequence probably came from that.