Left+right/up+down weirdness

I've found many games that do weird stuff when left+right and up+down are pressed at the same time. Thought it might be fun to make a list of some of the stranger ones, so here's the ones I can think of off the top of my head. Feel free to add more.

Battletoads - up+down in level 2 (vertical tunnel rope stage) kills you instantly
SMB - Mario runs/jumps in reverse on left+right
Spy vs. Spy - Character turns into an airplane on left+right
Zelda 2 - Link gains hyperspeed on left+right

Super Mario 2: Climb a ladder really really fast with Up+Down.

In first Tiny Toon you'll move forward really fast on L+R

Spy vs. Spy - Only for 1 frame do you turn into an airplane (finger on that pause button...)
Zelda 2 - You actually outrun the updating of the NT + AT...

I always thought the reverse jumping was a different issue (I think it's doable if you jump and start going backwards at the same time, the jump would get processed first making Mario not turn around when pressing the opposite direction in the D-pad until he hits the floor - can't recall well).

Could be. I have mostly seen it in TASes, which tend to use a lot of left+right weirdness, so I assumed it was something like that.

Well, there's a well-known bug that lets you get into the warp room (at the end of world 1-2 and 4-2) by jumping backwards through the wall. This is actually done on the real hardware, so I doubt it relies on left+right.

Also you can change the momentum mid-air (albeit with more inertia than usual), so you could technically just jump while idle then press backward...

Left+Right and Up+Down can be done on stock NES hardware, you just need a screwdriver to open the controller or to put extreme pressure on the d-pad to break it

I've been able to press Left+Down+Right on a stock third-party Super NES controller, as indicated by the control test in Kirby's Avalanche. I forget whether it was an SN ProPad or an SN ProgramPad.

Yeah, but I meant the trick was done without putting any effort =P Probably relied more on the physics quirks than any frame-perfect timing though (remember what I said about momentum while in the air).

Sik, SMB does run backwards when you press left+right. I did it on a famicom with an extra controller plugged into the front.

Being able to jump backwards is a different thing. It's not hard to do, or a bug, it's just that your facing is determined by the last direction held on the ground, regardless of the sign your actual velocity (which is easy to change midair, as well).

I didn't say it didn't happen, I said that jumping (not running) backwards can be achieved without doing it.