Walking through walls door glitch:

When you are facing a wall and there's a closed, but unlocked, door immediately to your left, right, or behind you, you can use this bug to walk through the wall in front of you.

If the door is on your Right side, press A+R buttons simultaneously.

If the door is on your Left side, press A+L buttons simultaneously.

If the door is behind you, press A+Down on the d-pad simultaneously (This requires that you remapped the Down button to take a step backwards).

The timing is a bit hard to get used to at first. To my knowledge it doesn't work next to empty doorways or locked doors. You have to be able to go through the door in question by pressing the A button.

Goat's Helm death warp:

Equip the Goat's Helm. Save the game. Rest. If you don't die save again and rest again. Once you've died and are back to the game's starting menu: Review your character (middle option on the left). Go to items and unequip the Goat's Helm. Hit B a few times to exit the menus and you should walk through the starting entrance doors.

(To note: I've had it fail when walking off a ledge at full HP after a grind, I think your current HP might need to be below a certain value for this to work as well, but I'm not certain if that's true and/or what that value would be).

Lock Picking the Ruby Eyeball Door (Bottom Castle Basement Level):

This one's a bit weird. Walk down the stairs from the castle's main level and fight the forced encounter next to the landing square. Doesn't seem to matter if you save/reload/reset or not after that battle. What DOES matter is you have to walk facing down the hallway, as opposed to strafing looking at the walls, all the way down to the end then turn to look at the Ruby Eyeball Door. After the text you have to turn left to face down the hallway and walk back to the 1st gate door. Use the Gold Key to unlock that door. Step up and hit "Y" which is set to "Open" now and choose the top option to lockpick the door.

Two things happen here: 1) the lockpicking display is flat on 0; or 2) the lockpicking display is showing numbers and green/red bar below them.

If you're seeing the 1st thing, try walking back down to the Ruby door, look at it and skip the text, then walk back to the door and hit "Y" to bring up lockpick again. If it's still "normal" and a static 0 and solid bar below it can try resetting and doing it all over again. In a speedrun setting though this is a hard reset usually.

If you're seeing the 2nd thing, keep hitting A until you unlock the door. Turn right back around and go through the door with A and turn left in the hall to walk down to the end and turn left to face the Ruby Eyeball Door. Press "Y" after the text and choose the top option to lockpick the door. Keep hitting "A" until it lands green and you'll step through the still closed door and have access to the river Styx.

"The Devil's Wind" bug:

In the Halls of the Dead, just before the path turns left into the Disko Zombie battle, there's a trap tile that sounds like rocks dropping on you. Sometimes it damages you, others it doesn't. Either way, from that step on until you RESET the game any time you step over a square that'd normally end up with you falling to your death you will instead float over it. If at any point you hit the reset button this bug ends and that trap tile does not reset to re-enable it.

The run currently uses this to float over the pits in the Temple of Ramm to skip most of the battles and avoid needing to get the Staff of Ramm. If you're going to die after this tile in a run, let it happen and reload from after the death screen. The bug will persist through death.

Fun fact: It will persist even when creating a new save file (even after deleting the file that enabled the bug) if you haven't reset the game.

Dying to clear some encounters:

I don't fully understand why, how, when it works, but there are times when if you die and reload (not reset) before certain forced encounter tiles the game effectively despawns that forced encounter.

The route I followed does this very early to skip the encounter in the room with the copper keys (Castle Upper Level near Northeast Tower Steps). It also seems to clear the Lesser Demons encounter by the fountains after opening Mino's Gate (Save, equip Goat's Hat, Rest until dead, reload).

I've read it's supposed to reduce/remove a lot of random encounters too, but I haven't really noticed that to be the case. It also does not universally affect all forced encounter tiles, only those two specifically that I'm aware of.