Access Glitch Worlds in Super Mario Bros. via NES Tennis

How can you get to glitch worlds in Super Mario Bros. by using the game Tennis? It's all explained right here.
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[RGMechEx]

Some common Q&A's I've noticed in the comments!

1. Will this work with the SMB+Duck Hunt cartridge?
It will not, since the game selection screen clears all of memory before you can get to Mario. However, the SMB+Duck Hunt+World Class Track Meet 3-in-1 cartridge doesn't clear memory, so it will work on this version!

2. Doesn't this only work on the Famicom?
Nope, it will work on the original NES as well! This is a common misconception. The trick was originally found by Japanese players, so a lot of the information came from players using a Famicom. Like the video states, even with the CIC that flips the power on and off, power to the system's memory is retained, which allows the trick to still work.

[LarpingGecko]

Never knew holding "A" when you pressed start let you continue from the last world. That would have been handy as a kid when it came out lol.

[darakstriken]

This reminds me of that crazy "Stop 'n Swop" method of performing Arbitrary Code Execution in Paper Mario. It uses some glitches in Ocarina of Time to setup RAM, and then swaps the cart over to Paper Mario quickly enough that the prepared RAM doesn't decay. Cool to see a similar trick used here, and get a technical explanation of it.

[DctrDRK]

As a kid, I remember cartridge swapping from some other game to 3D World Runner. It immediately played the ending to the game. I was amazed by it, but I could never reproduce it again. It's really great to know existing RAM values from the first game must've been the reason.

[Sinn]

I didn't know you could do this with an Nes but the Sega Master System and Genesis...oh yes. My favorite thing to do was plug in Altered Beast in my Genesis, starting it up, waiting for the blue Sega logo to appear, pulling the cartridge from the console, inserting Space Harrier 2, and getting 50 lives at the beginning of the game! I have so many more stories of this kind of thing happening that I could be here all night. Neat episode!

[sourlemon]

2:18 I LOVE how you accurately pointed out which pins are used for receiving power. Fine details like that get my nerd juices going.

[SuperSmashDolls]

I remember hearing that this glitch was rather famous in Japan and that magazines had Famicom BASIC listings that would let you setup a cartridge swap manually. I don't remember if American magazines cottoned onto it or not.

Also, I'm pretty sure this particular glitch is why the SNES and Game Boy both had physical interlocks to prevent you from swapping cartridges with the power on. I imagine Nintendo also got PTSD flashbacks when Rare said "hey what if you could swop cartridges to move items between two games".

[Dang_Ol_Username]

I was a Playstation kid growing up. I remember doing this for GTA 1. If you were loaded into a city, remove the disc and insert a music CD of your choice. The radios now play the CD tracks.

[ClassicGameSessions]

The technical explanation is good and makes sense, would never have guessed the correlation between the two games to trigger the glitch though. Look forward to the next episodes on this!

[TrueN-bit]

I'm glad I finally got an answer on why this happens. I remember hearing about this years ago (I think it was on an episode of "PopFiction"?), but they really didn't go super in depth on why it happens. In fact, I think they said it's random where you go. But since it's based on number of foot step sounds, that sounds actually pretty easy to control. Nice video! Looking forward to part 2.

[Tomsonic]

I used to do this quite a lot with Sega Genesis games. One particularly useful trick was to transfer the much easier Sonic 2 level select and debug unlocks to Sonic 3, as Sonic 3's cheat code was VERY difficult to get working. Just unlock them in Sonic 2, swap cartridges with the power on and press Reset - it works because all Sonic games use the same memory addresses for variables like this!

[MrCheeze]

From your explanation of what all the bytes do, it seems entirely plausible that there exists some game that writes directly to the "enable world select" byte without corrupting the score or the A5 magic number. If so, it may have never been discovered because enabling world select is a much less flashy effect than loading glitchy worlds.

Alternatively, maybe cycling the power will occasionally cause the "world select" byte to decay to nonzero without yet corrupting the A5 on some consoles!

[ipaqmaster]

You were right it was interesting! Always loved cartridge swapping, tilting and the other things you weren't supposed to do with them

[lordfarquard]

I love these technical explanations man, you're really rocking it out of the park.

[universalperson]

I first saw this trick mentioned in an issue of Tips & Tricks magazine.

What's fascinating is that in Japan this glitch is as popular as the Minus World, if not more so. It also inspired World 9 in Super Mario Lost Levels.

[ahoustonpsych]

What a fascinating topic and execution. This is the kind of stuff I'm here for. Love to see how your style and animations are progressing - everything is looking top tier as heck these days! Great stuff!!

:)

[james-m-]

I just watched Kosmic’s video playing with this glitch, and was super curious how the memory structure worked. Excited to see the next segment, since the level alterations are honestly the oddest part

[WanderP]

This channel is so good because the concepts are explained so well and are applicable to many other areas of low level programming outside of video games.

[Hezkun]

I'm so amazed at how deep and technical your knowledge is on the console, thank you so much

[doublecontralto]

A different but somewhat related trick was actually the lesser known (and significantly easier) of two ways to access the stage select screen in Sonic 3 (by itself, *not* when locked-on to Sonic and Knuckles).

You'd need a copy of Sonic 2, enter the level select code on that game (go to the sound test in the options menu, and enter 19, 69, 09, 17 and press start), then remove the cartridge without powering off the Genesis, put Sonic 3 in, press reset and when the title screen came up, pressing down twice would reveal a "Sound Test" option, which just so happened to have the level select. IIRC some of the S&K stages were listed as well but you couldn't actually select them.