I thought I'd post this question in the forum with the most accumulated knowledge of Metroid NES's inner workings. I apologize that it's not technically speedrun-related, but I haven't been able to find an answer anywhere else.

I recently acquired a first-edition, five-screw copy of Metroid, with the intention of getting all five endings. However, after leaving the game on and unpaused overnight for well over 10 hours, then completing it, Samus merely waves to the player in her full suit at the end. This is supposed to be for completing the game in 5-10 hours, whereas after 10 hours, she supposedly turns her back to you at the end in shame. I tried playing it again, this time without getting 100% of the items, but got the same 5-10 hour ending despite leaving the game running for nearly 24 hours. Can anyone explain why this happens?

I just tried password Ktj-tO Pf0m03 l-yqHG 00y016 which is supposed to be 20 hours, 59 minutes and 48 seconds and got the 5-10 front facing "wave" ending instead of > 10. It also had strange drops from the monsters in tourian. :)

Silver label, 3 screws REV-A.

I wonder if the reissue with different artwork has the other ending?

edit: here's a link to the password generator if it is useful to you https://www.truepeacein.space/

You can get this ending if you beat the game with the Justin Bailey code (JUSTIN BAILEY ------ ------) This works on the Rev. A cart (grey label) and I believe it also works on the Yellow Label re-release cartridge though I can't test that. I guess this "worst" ending is for the dirty cheaters out there!

The weird drops issue Retrogaming2084 got is because that password spawns you in Tourian without the appropriate globals being set to the correct zone... it still thinks you're in Brinstar. If you ride the elevator up and back down after spawning it'll fix that.

All right, after a bit of research, I've concluded that the worst ending actually triggers not at the 10-hour mark, but the 37-hour mark. I pinpointed the exact amount by starting at two extremes and narrowing it down, using passwords from https://www.truepeacein.space/. This works on every OG cartridge I've tried, as well as emulators.

The reason the Justin Bailey code triggers it as well is because this password is not hard-coded with any special parameters. It has its own timer attached to it, which is actually set at 5090331 hours, well-past the 37-hour requirement!