This is done without outside cheat devices.
Ocarina of Time - Arwing

Over the past several weeks, the speed running community has absolutely broken open The Legend of Zelda: Ocarina of Time. The record for Ocarina of Time any% went from just shy of 17 minutes as of six months ago, to just 12 minutes and 3 seconds as of 4 days ago. To put it into perspective, it took the community over 4 years to get the old record to be under 17 minutes. It's taken them six months to get it to just 12 minutes.

For a game that is 22 years old, shaving five minutes from a record is an incredible amount of time saved. This was all accomplished thanks to a trick that allows runners to skip directly to the game's credits. This bypasses the entirety of the game, including all boss fights. This article from Kotaku goes into the details of this new trick.

The short of it is that players found a way to do some very specific actions that can alter the game's memory values. It's called arbitrary code execution, or ACE for short. At its core, it's all very technical but when it works, it looks a lot like gaming magic.

If you want to see what that looks like, you can watch the current (as of January 24, 2020) world record run for Ocarina of Time Any%.

It is because of this new technique that runners have been able to find another secret that was once considered one of those fabled "playground rumors." We all had them: A friend that would say their relative worked for Nintendo and that they were told about some ultra super secret that nobody has seen but they totally have!

One such rumor said that it was possible to find a working Arwing from Star Fox 64 within Ocarina of Time. Totally not real, right? At the very least, you wouldn't be able to see it without the use of a GameShark or some other cheat device. That was the case until this week.

An Arwing is now able to be spawned into Ocarina of Time through similar methods to how speed runners are able to beat the game in 12 minutes. By doing very specific ACEs three times with specific file names being used, players can now spawn in a mini Arwing. In the clip below from Zfg1, you can see how it is fully modeled, moves around, attacks Link, and even has special effects tied to it.

(via Reddit)