Assassin's Creed Valhalla

The first piece of this achievement is actually unlocking the Draugr's Toll Outfit. This is unlocked automatically during the Dokkerland side quest required for Freedom Fighter (40G), so make it a point to complete that side quest during one of your first runs so you have this Outfit available. Note that this outfit, along with its benefits, carries a disadvantage in that it reduces all healing effects by 50%. This mean elk shrines and elk antlers from vendors only heal you half as much as they normally do. That is what makes this achievement more of a challenge than the others.

With the outfit available, there is some preparatory work I recommend doing before starting the run where you attempt this achievement. First, ideally, it would be a good idea to earn enough Thoughts from beating bosses in previous runs such that you can fully upgrade the Draugr outfit. This will greatly improve its armor and make it so you take much less damage during your run, helping offset the reduced healing. Secondly, amass enough Memories (should only take one run to do so) that you can buy a number of Nar's Favors before this run. Namely, you'll absolutely want to purchase the Favors that increase the number of elk shrines and mark them all on your map. I also recommend purchasing the Favor to reduce merchant costs by 30%, so you can buy more health, runes, and weapon/health upgrades from merchants. If you had a good weapon in the previous run, you can also buy that Favor to use it again this run. Just know that you only get the base version of the weapon even if you had it fully upgraded in your last run, so you'll need to upgrade it all over again. Lastly, from a preparatory perspective, complete the side quest in Kaldstad discussed in Freedom Fighter (40G) if you haven't already, since this grants you a free revive in each run. This is critical to success.

With that all done, you're ready to start this run. Your biggest asset for success here is going to be taking advantage of the save exploit to ensure you reload in case you really mess up and take a lot of damage and/or die. Here is how the exploit works:

The game autosaves right after you complete every encounter in this DLC, as well as right before every boss fight. What this means is that you can quit out and reload your save whenever you feel like you really screwed up, took too much damage, or even died. For example, you're having a great run and then those druid enemies in Nidheim really destroy your health with their fire attacks after you screwed up some assassinations. Rather than being stuck with the results of that fight (such as all the health you lost), you can pause and quit to the main menu, then continue your game. You'll be back to just before you started that encounter, allowing you to reattempt it again, hopefully with better results. You can use this during any encounter or boss fight to ensure things go better for you, or just that you succeed and don't die.

There's no need to be so conservative that you're reloading your save every time you get hit. Personally, I would only allow myself a maximum of two hits per regular encounter before I'd reload. The first and second boss fights have a little more leeway since there is a guaranteed elk shrine to heal after each one. The third boss fight, the dragon, is the roughest one. Not only is it really easy to take a ton of damage, but there aren't any elk shrines throughout the fourth area, so you won't be able to heal much. My recommendation is just to ensure you don't die and use your revive during this fight. As long as you survive it, there is a guaranteed elk shrine right at the start of the fourth area, and then a coin merchant halfway through the fourth area where you can buy some health too. That way, you should be able to go into the Hel fight with at least half health, plus your revive with another half health.

Those are really the main tips unique for this achievement. I also recommend reading through my tips in The Queen's Fall (20G), as they all apply to this run as well.