These tilesets use 16x16 tiles and the proportions are designed for character sprites around 32 pixels high.
All tilesets are in PNG format.
The main sheets are usually 256x256, but a few are larger.
Environmental objects (trees, rocks, furniture, etc) are also on smaller sheets prepped for grid slicing.
Every image has been set to a PPU of 16, with no filter mode, to preserve the appearance of the pixel art.
Every image has been pre-sliced.
No Tilemaps are configured (I'm new to Unity and prefer to use Tiled for mapmaking).
Many environments come with image guides or text files to help demonstrate some key concepts.
Many environments come with a sample map constructed in Tiled (a free map editor I recommend).
You may use these assets in any game engine, not just Unity.
Important user license clauses include a prohibition against use in web3 or genAI games. Read the particulars here if that concerns you.

Mana Seed Pixel Art Tileset Collection