From the author's README on Thunderstore

Geralt of Rivia (The Witcher 3)

Geralt from The Witcher 3: Wild Hunt as a full-body costume for skate., running on ReSkate.

Find him under Apparel → Costumes.

What you get

Geralt in his Witcher armour, with both swords on his back, the wolf medallion, gloves and boots.
Fitted to the skate. skeleton, so he uses the game's normal animations.

Known limitations

His hair is drawn solid, without transparency, so its edges look a little chunky up close.
The face does not animate.
The model is more detailed than the stock characters, so it is heavier to render.

Install

Install from the MODS page of the ReSkate launcher, or extract the zip into its own folder inside Skate\Mods\.
Enable the mod and start the game through the launcher.
Open Apparel → Costumes and equip Geralt.

Built for skate. Steam build 25617022.

Credits

Port by Ethan, made with Blender and ReSkate Studio. AI coding assistants were used for the conversion.
Model and textures from a Witcher 3 Geralt model shared on Sketchfab.
Geralt of Rivia and The Witcher 3: Wild Hunt belong to CD PROJEKT RED.
Unofficial fan mod. Not affiliated with or endorsed by CD PROJEKT RED, Electronic Arts, Full Circle or the ReSkate project.

Install Geralt of Rivia

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Geralt of Rivia and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.