I mentioned this in my
Steel Heart guide, but I managed to get this during my first Steel Soul run.
This achievement is based on knowledge of the game and being able to go through it quickly. Not super hard, but can take a few playthroughs before you're good enough
I outlined some good goals to get completion fast in the above guide, but I'll copy/past the list here:
A short list of what to aim for, completion-wise. These not only help boost the percentage, but can help you during the game:
- Equipment. These are all of the basic abilities you get (Mothwing Cloak, Mantis Claw, etc.), and half of them aren't even required to beat the game. You gain 2% per piece, for a total of 14% if all 7 are collected. Plus, you'll have much more maneuverability.
- Spells. The abyss versions of each count as 1% extra completion (6% total for getting the base spells and their upgrades). Plus, they help a lot during combat. Especially Descending Dark's i-frames and insane damage output (upwards of 88 per use if you have Shaman Stone and every shockwave hits).
- Masks and Soul Vessels. The Grey Mourner's mini-quest can be a massive pain, but it's worth it. Especially if you clear the path beforehand (most enemies don't respawn until you rest on a bench, so all that's left are the small weak ones).
The extra health and soul storage is invaluable, and each full mask (and vessel) counts as 1% completion (if you get all 3 vessels and all 4 masks, you get 7% completion in addition to more survivability)
- Nail Upgrades. Not only does each upgrade boost your damage, but each one counts as 1% completion. 4% total if you get all 4 upgrades, and you'll deal 21 damage per swing (which can be increased to 31 using Fragile Strength)
- Nail Arts. The platforming can be a bit of a challenge, but each master has a bench before you meet them. Each art counts as 1% completion, and can help in combat.
- Dreamers. You're required to get these anyway, but each one counts as 1% completion. Nice.
- Charms. You can get 36% completion if you collect every charm, and most are rather easy to get. (but the ones that replace an existing one {e.g. Unbreakable Strength replacing Fragile Strength} don't give any extra)
Note that dying in the White Palace still counts as an actual death. And the Traitor Lord is a difficult fight, so getting Kingsoul probably isn't worth it (both halves need to be gained in order for it to count as a charm and thus give the 1% completion)
- Trial of the Fool counts as 1%,, but it's long & grindy so it's not worth it. If you want the achievement, do it in a regular save.
- A bit of an add-on to the above, but doing the Trial of the Warrior and Trial of the Conqueror will help. You'll get a Charm Notch and Pale Ore, respectively. And each one counts as 1% completion.
If you do everything on this list, you'll gain 75% completion (my math might be a tad off though). That's already 3/4 of what you need, and I didn't even mention any of the boss fights that count. Nor the Godhome content.
PS: Not sure if this is even possible, but if you're fast enough you could get
Speedrun 2 at the same time as this one.