From the author's README on Thunderstore

A shark-mouth backpack cosmetic mod for ReSkate / skate.

Installation

Open the ReSkate launcher.
Go to Mods, then choose Install .zip and select this package (or install it from Thunderstore).
Enable the mod and launch the game through ReSkate.

For manual installation, extract the contents of the package into a single mod folder inside ReSkate/Mods/ so that layout.toc, initfs_win32, and Win32/ are directly inside that mod folder.

Notes

Contains a ReSkate Studio native patch. Compatibility depends on the game build it was made for.
The original asset files are preserved from the supplied ZIP.
Do not install the original ZIP and this package together, as they contain the same patch.

Install SharkBackpacks

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

Open ReSkateLauncher.exe and go to MODS.
Search for SharkBackpacks 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.