Shovel Knight: Treasure Trove

The premise of this achievement is pretty simple: complete the game without collecting any Will or Darkness upgrades. They're easily avoidable in the stages -- just don't break the big green or blue chests.

There is nothing to limit your use of curios, however, so I would highly recommend the following:
- Will Skull (upgraded) to recover your health for surprisingly little Darkness cost
- Judgement Rush (upgraded) to entirely skip platforming sections with conveniently located enemies or as a panic button if you're falling to your doom. Note too that activating the Judgement Rush when there is no enemy nearby resets your wall climb.
Other curios can be used of course, but I found those most useful by far.

Another purchase I'd recommend is the Raiment of Risk. That's the one where destroying a checkpoint reduces your Will but grants a ranged scythe slash with increased damage and Darkness regeneration. The bonus here is that since your Will cannot exceed 4 for the achievement, you don't actually get a health reduction. You basically get all the benefits at 0 cost (aside from breaking the checkpoint). If you're confident in your abilities, this is the way to go. The Darkness regeneration coupled with the upgraded Will Skull means you should only die to platforming fails, never to an enemy or boss.

All in all, there are only really two difficult fights -- Shield Knight, and the Enchantress, since you cannot use your Raiment of Risk for either, and you have no health regeneration options at all for the former.
- For Shield Knight, I found a useful tactic was to use my slash on her shield to "bounce" behind her and then slash again in the back. When she throws her shield, jump over it and get as many free hits in as possible
- For the Enchantress, I found being aggressive to be the best strategy. Taking damage isn't a huge issue since you can regenerate your health with each use of the Will Skull, and you can still recover Darkness every few hits you get on her.

Lastly, it is worth considering combining this run with the Make a Killing achievement (finish the game with 60,000 gold without replaying any stages or minigames). I was able to buy the Raiment of Risk (5000 gold) and upgrade my Will Skull and Judgement Rush (4000 gold each) and finish the run with 64,000 gold. I did, however, have to be very conscious of my gold collecting and quit out of levels if I died and couldn't recover my gold.