The Shadow Slime is formed by leaving a Phosphor Rad Largo out in the sunlight, or, leaving a Phosphor Rad Largo to bake in the sun, which ever one you like to use.
Shadow Slimes adds a new slime type the Shadow Slime. This section will go over all 3 of these mods. All 3 of these mods were published recently (as of 12/31/20).