Initially found in a small hovel in the room accessible after defeating Gruz Mother in the Forgotten Crossroads, slowly succumbing to the infection. Talking to him breaks him out of his daze, and he will return to Dirtmouth to open his shop.
After given the Shopkeeper's Key, more of his goods will be unlocked.
Visiting him after learning all three Nail Arts, he will be found in his storeroom, where it is revealed that he is the Great Nailsage who taught the three Nailmasters and rewards the player with the Nailmaster's Glory Charm.
...Esmy... how much deeper do we have to go...
Oh! What?! Who are you?! ...I see. This old village. What a strange dream, to have led me down here! If you hadn't found me, I don't think I would've ever woken.
I'm Sly. Usually, I live an uneventful life up in Dirtmouth. The air in these ruins doesn't agree with me, so I'd best be getting back. If you return above, come and see me. I'm probably the friendliest face left there, and I can thank you properly for your good deed.
Dream Nailed in the ruined village:
First entering shop
If you're planning a trip below, I've several items that may improve your chance of survival.
After Iselda opens her shop
Perhaps I should start to sell maps as well... or is that a little aggressive? Heh. All's fair in a world made of Geo.
Nothing to sell
I think there might be a few old trinkets down in my storeroom, but I lost the key a while ago.
So, no more business between us I'm afraid! For now at least. Get out of here and let me spend some quality time with all the Geo you've gifted me.
Back again? You know I haven't any stock left, yes? You've cleaned me out.
Or were you hoping to sneak a peek at my mountain of Geo? Well it's mine now! And fairly traded.
When player has Shopkeeper's Key
Hmm? Did you find it in those old mines perhaps? Very curious. I've no idea how it ended up in such a remote place.
Very honest of you to return it to me, yes. Very kind. And now that I can open my old storeroom up, I can sell you some of the rare stock that's been gathering dust in there.
These items may be a little time-worn, but they still retain their full market value. Very precious stuff! Take a look...
While the Grimm Troupe is in Dirtmouth
Dream Nailed in his shop
After learning a Nail Art
Ah! The way you hold your nail! So you've learnt a Nail Art...
Very interesting. I wonder, do you have the passion to continue your training?
After upgrading the Nail
Hmm? Oh, this is the same nail... but it's been honed! By someone extremely skilled...
A nail is an extension of ourselves, it is the instrument by which we shape the world around us. It's a sacred duty to keep its edges sharp.
...Heh, sorry. I shouldn't ramble on like that. Let's talk Geo instead.
After learning all Nail Arts
I have a gift for you, warrior. As a shopkeeper, I admit parting with it for free is rather difficult.
But as the Great Nailsage I must recognise your skill. You have mastered the arts of my remaining pupils. Now tradition decrees you too may hold the symbol.
Wear it proudly, Nailmaster. You shall be the last to receive its like.
Nothing for free at least. I'll be up briefly and eager take your Geo in trade for my precious wares.
If you see your fellow Nailmasters again, tell them I carry them in my thoughts always. And that they should come and buy something from their old teacher as a mark of respect.
Dream Nailed in his basement
Sly first appears in an abandoned house in the southeast region of the Forgotten Crossroads. After talking to him, he can next be found in Dirthmouth.
- According to a livestream Q&A, the development team originally planned for Sly to be a difficult boss who wielded a nail approximately the size of the other Nailmasters'.
- Sly being more than he seems is repeatedly foreshadowed. For instance, his very first line - "Oro, you oaf... you wield your nail... like a club..." - refers to Nailmaster Oro, he states that he is "usually Sly", and he comments on the player's Nail several times.
- Sly is the only merchant that requires the player to purchase an item to unlock the next one in the series.