You unlock speedrun mode after you beat the game once. Before you attempt this, go to settings and play around with screen shake and hit pause. I left hit pause at 50% and disabled screen shake completely. This is just for preference though, it has no bearing on completion times.
Afterwards, go back to the main menu and hit the speedrun button. This is the most important part. There are a few options you can enable/disable. Enable Action Only, disable Cutscenes, enable skip replay, show timer and death count. You can also change the swords (if you unlocked them). I played through with Master Sword. In think it's easily the best of them since the projectile usually hits enemies behind doors if you hit them open. It's also a massive help against the final boss since you can hit her with it while she charges her beam.
That's it for the settings.
There are no fixed times/deaths for gold medals, you just have to play through and get lucky at the end. All that counts is the amount of gold (or even better, platinum) medals you collect through the run. I believe the game averages out the medals at the end to give you the final score. I have no idea if the final time has any bearing on the final medal. These are the times I achieved for a gold run.
Some random tips:
- You should take advantage of the fact that the first few levels are easy. Try to rush through with 0 deaths. I find that it's easiest to get a platinum medal for Factory, Hotel and Prison. This should give you some room to mess up later on.
- Try to use slow mo sparingly. The timer still moves at normal speed, even if you use slow mo so it's a huge waste of time. I only used it against shotgunners and the shield guys + against most bosses.
- Look at some speedruns on youtube. They usually have perfect routes and a few other tricks I didn't mention (small exploits to get a few seconds of advantage)
All in all, dying doesn't matter too much. What's most important is completion time. Try to focus on that.
Apparently deaths do matter when it comes to platinum medals. A platinum medal is only awarded for a gold time run + 0 deaths. There is still some room for mistakes though as you can see from my scores.
- Don't use the gimmick swords like claymore or phoenix. They are way too slow. Either use the standard katana or master sword. Master sword is identical to the katana and prism sword, only it fires a projectile that can kill any unarmored enemy. Try not to rely on it too much as it needs to recharge after firing.
- Try not to take it too seriously. It's incredibly easy to mess up during the final half of the game and even a small error can be enough to tilt you.
But above all: Good luck. I don't know why but the times to finish for gold medals are brutal and leave almost no room for error.