I've seen some very rudimentary debug features in Zelda 3 and I know of some fairly intricate ones in Super Metroid that I've been told about. Super Mario RPG has a debug room, not sure about a mode, though. I figure most games have some shortcuts or debug features left, otherwise the developers would have had a harder time making the gime.

While playing Marion 64 DS I once happened to crash it (I was backflipping onto a bob-omb with mario while it exploded while also being hit by the rock smash thingy). Then something like a "console" opened in the very top (one line, black background, light green text color), pretty much displaying nothing except like 3 characters...
Game couldn't go on and the stuff on the top didn't seem to want to do anything...

But yeah... that's the Tau way... Crash stuff

cYa,

Tauwasser

Emerald Dragon (SFC) has one. It only partially works. I imagine it fully worked prior to the final release, though from the code I've seen, I wouldn't be surprised if they never could get a full functional debugger with some of the bugs they left in that game! I know I've seen a few others, but I don't remember them off hand.

Often times debugging functionality is purposely left in to be accessed via cheat codes. Back in the NES days, many of those stage selects or health code cheats were just left over debugging routines left in. I've read that in interviews with past NES devs.

While hacking Dragon Ball Z - Super Gokuuden Totsugeki Hen for an eventual French translation, I found a debug menu.

It is enabled by NOPping a branch at the end of the reset handler.

If you find this let me know... That could be useful to me right now.

Also of note: Paper Mario (N64) had a few debug rooms accessable via GameShark and one of the rooms said ''MARIO RPG'', Which means it was originally a game called Super Mario RPG 2. And during development of Paper Mario, It was meant to be for the failed Nintendo addon called the 64DD

I found something like this a while back in an obscure PSX flight sim called "Wing Over". I was trying to put in a cheat code, but I ended up doing something different (and twice as long) and it opened up a couple of dev options in the title screen: "Demo Edit" and "Ground Edit"

I'm not sure how they worked (the menus for those were all in Japanese), but Demo Edit seemed to let you play around with the attract sequences, while Ground Edit let you edit tiles. Or something like that. Since I haven't been able to unlock those again, I might have to try hacking it open to see.