Ring of Pain

This method requires a couple of items that are unlocked from other achievements, but none of those are too difficult to get done.

1. First you want to do "Stone Touch" for petrifying 50 enemies, which unlocks 'Stone Scream'.
2. Next you'll be looking to get "Soul Stash" for having 2000 souls at one time, which unlocks 'Soul Scream'. If you've got the previous item, this one isn't essential, but it adds an extra item to the pool for you to hopefully find.
3. Finally, it'll save some time to have earnt "Illuminate, Eliminate" for beating the light ending once to unlock the 'Double Candle'.

Once you've unlocked those, it's time for RNG to be the hardest part of the run.

If you unlocked it, start the run with 'Double Candle' and choose 'Hermit's Tiara' as your starting item. If you don't have it, then just keep restarting and opening chests until you get the Tiara. This will freeze enemies on hit as long as you have 4 or less items equipped(including your candle annoyingly). The best thing about this item is that as long as you're faster than what you're attacking, you'll keep freezing it and never let it retaliate. Your main goal stat wise is getting speed up to 27, since this outpaces all regular enemies in the game. There are some special enemies in the boss sections that are even faster, but by such huge amounts that you can't beat them through just stat boost pick ups so we'll be dealing with them via our item strategy. Don't worry about attack, lower is actually better for the build. Ignore defence entirely since we should never be taking a melee hit. Health and clarity are good to keep up if possible, but focus on them after reaching 27 speed.

The main thing to remember is DON'T just pick up any old items. You only have 2 free slots left in order to keep the freezing power and the build needs both.
For any free white item cards, keep picking them up and using the free re-roll to try and find 'Weightless'. This isn't an essential item but it helps a lot in early game by massively boosting your speed from lack of other items. If you find another mask then feel free to take it, but weightless is the more helpful and you'll hopefully be replacing it with a purple(epic) quality one later anyway. If you do get weightless, don't forget that you'll lose it's boost when you swap to the other mask later, so aim to get your speed up to about 33 with it.

Keep going until you start finding blue(rare) chests and items. From these you'll be hoping to get one of the two spell books I advised you to unlock at the start of the guide. Each deals just 1 damage, but if it kills an enemy, the damage is permanently increased by one. You'll be using this to kill everything you see from now on. Getting one of these early can stack up to 200+ damage per use by the final boss. This is where the lower damage helps us, since only hitting for 1 point means we can charge the book very easily and also control enemy health to get the book damage up quickly.

Finally for the setup, when you see purple(epic) items appearing, you're going to want to look for a mask called 'Camouflage' which stops ranged enemies from attacking at all. If you've raised your speed up enough, you'll probably realise by now that the only things hurting you are the ranged enemies, so this mask completely removes them as a threat and also makes the first end boss a walk in the park. This one isn't 100% necessary like the other items as long as you have enough health to take the hits, but you won't be looking for any other items so may as well spend the souls looking for it and it's just a useful safety net to stop premature run endings.

And now that you have all those, on to the boss fight, which should give you no trouble. My only note is that this is where the much faster glowing enemy variants appear so be careful not to just attack wildly. Make sure to use regular frozen enemies to charge your spell and one shot them out of the way. If you beat the light ending once anyway, you should know what to expect, but I may as well outline the way each stage works.

1. Confidence: Can shoot at you. This is the main reason for wanting camouflage, but if you have a charged spell and more than 24 health you can just tank charge at them and insta-kill them.
2. Connection: KILLING an enemy raises Connection's stats by 1, HURTING Connection raises a random enemy's health by 25 and damage by 10. Don't worry about the raise in Connection's stats, just move around to them and one shot them too.
3. Discipline: Is very strong but weakens on every hit. Completely useless ability when you can kill them with the spell.
4. Calm: All enemies start frozen but each turn one will thaw. Just charge at Calm over the frozen enemies and kill them quickly to stop more from thawing.
5. Vision: Every time you attack Vision, a single card is obscured. I personally killed everything here first so nothing could catch me out at the very end, then one hit killed Vision too.

And that should do it! I realise this is a lot of information to go through, especially if you've just started out and haven't gotten to grips with the game, but this was absolutely the most broken build that helped me get a vast majority of my ending achievements. If there's anything you think I missed, please let me know via comment or DM and I'll do my best to update this.

Best of luck!