@coolboymew At first, I thought this was an unused level that was in the final ROM, but was left undiscovered for over 25 years, but it turns out that this was in the gigaleak, which he didn't mention.
It's only playable now thanks to the decomp.
@coolboymew According to TCRF, it is, which makes sense because I highly doubt that a scrapped level in the final ROM would be hidden for that long.