HAND is a supplement for FIST that expands the downtime between missions. The vibe is maybe a little bit Midnight Suns.

The PDF is 50 pages (!!) with a clear, well-organized, technical document style layout.

Contents-wise, there's a lot here, but the core mechanics are simple. Between missions you can take actions to gain War Dice, gain temporary weapons or armor, temporarily alter weapons and armor, and permanently boost attributes. So, what else fills the fifty pages of this supplement? A unique downtime action for every Trait, of course.

This is a wildly ambitious thing to add, but it contributes a considerable depth of flavor to HAND. All of the Traits interact with different downtime actions in different ways, and all of these interactions fit the character of the Trait in question. Weaponmaster lets you gain temporary type immunities to weapons. Psychometry lets you automatically locate item hotspots.  

Overall, this is a really cool supplement that goes far deeper than I expected. If you want to add a ton of unique content to FIST and give the players a little more flexibility between missions, this is well worth picking up.

Wow, amazing amount of work on the D666 table, really wanna try this out in my own games sometime but I've only run one-shots so far so this is good incentive to plan a campaign!

HAND is an expansion of the downtime rules from the Ultra book that puts significant mechanical heft into between-missions activity as your merc prep for the next adventure.

It's 50 pages, and most of it is, frankly, a herculean effort in adding specific downtime bonuses and abilities to EVERY SINGLE ONE of the d666 traits. The rules are solid, the trait addenda are evocative, and the helpful Edge Cases section at the end is very useful.

I also like that NinjaDuckie really leans into the bonkers on this - using this supplement RAW, your players can make their characters super beefy (at least at the beginning of the next mission!) to make for even more chaos at the table.

One of the best side-effects of a guide like this is by extending EVERY SINGLE ONE of the d666 traits, it gives players incentives to make different choices and unexpected results if rolling on the table. For the min-maxers it adds complexity, and for chaos gremlins (hello!) it adds an entire new layer of shenanigans.