It hasn't been tested in GMS2, but you should have no issue importing the spritesheets. Most sprites and tiles are in 32x32 pixels, or multiples thereof.
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Visit the green hills, chill at the snowy mountains and don't forget to bring sunscreen to the desert dunes!
Retro Pixel Landscapes is a high quality tilesets asset pack, bringing variety and life to your 2D environments. It features 3 biomes; grass, snow and sand. Each biome features 3 sets of wall types and a set of decoration objects each. Make your very own, retro inspired worlds easily with the Unity Tilemap-ready assets! Also available for other engines as spritesheet images.
Feel free to leave any comments, feedback or suggestions here or on the asset page. I'll be opening up all my asset packs to have comment threads, as I have more time to be able to moderate and respond to them now.