There's DLC, and then there's this DLC.

Hadean Lands is an interactive fiction game done in the old adventure game style. There are no graphics. You simply type your commands and read what happens next.

Hadean Lands came out in October 2014 and was received positively.

Here's the setup:

Marooned in an alien, airless wasteland - your starship fractured - your crewmates missing. Can an apprentice alchemist learn how to survive?

And here's how it works:

Hadean Lands is a game of alchemy and exploration, with an intricate structure of interlinked puzzles. Every ritual you learn adds a new ability to your toolkit. But every ritual requires a different combination of ingredients, and some ingredients are in desperately short supply.

It's important to note that Hadean Lands does not come with hints or a walkthrough, because that's what this DLC revolves around.

The £26.99 DLC, which came out yesterday, is a certificate that says you, the player, promise to finish Hadean Lands without looking at any hints or walkthroughs on the Steam forums or anywhere else on the internet.

That's it.

The certificate with a sample watermark is available to download free from the DLC's Steam page.

The idea is you print out the certificate, sign it, and hang it on the wall. The DLC does not affect the game in any way.

The developer, Zarfhome Software, took to Hadean Lands' Steam page to explain further in a FAQ. It's pretty amazing.

Is it all a big joke? Well it seems like it is, but there's real world money changing hands here. Here's a comment by the developer on Steam:

Either way, the DLC seems to have gone down well with Hadean Lands. Here's a snippet of the response:

What next? Horse armour? Oh wait...