The Steam Loyalist Upgrade Guide by Oni das Alagoas

This DLC brings cosmetic items. Only two of them changes mechanics in the game (Enchanted Burrwitch Brew and Will-O'-The-Wisp), althout the changes do not have a big impact.

These are the five helmets that come with the DLC:

The Powdered Wig
The Pillager's Dread Helm
Helm of the Venerable Warrior
Helm of the Southern General
and The Admiral's Hat

The Swashbuckler's Coat is the only clothing listed in the DLC.

Here is a picture of it in-game:
And a closer look at the clothing:

As said in the store page, Will-O'-The-Wisp pet acts as a light source in the dark. Here's a pic of it in-game:

It's stats:

With and without the wisp comparison:

With Without Wisp Aura:
The Burrwitch Brew is a booze/lichor that makes your character drunk when you drink it. It lasts 450 seconds (too much huh?!) and stuns your char from time to time while on it's effects.

It's stats:

I hope this guide explained everything you wanted to know. If you need some more information, be sure to write it down in the comments.

Cya.