I have seen the boss from game Midnight Horrors and I really want to know the methods to create slimy and color texture like this boss(the weapon too).
Possibly, setting up a PBR texture can help you achieve that look. Depending on your knowledge of texture painting, you can make a texture out of base colour, normal, roughness, metallic, and height maps.
I would suggest having a look at some YouTube videos under PBR texturing, depending on what programme you are using.
This can be easily done in Substance Painter, from what I know, but it is a paid programme.