Mix Shader between values of 0 - 0.5 is the same as 0 What I am trying to do is a glowing transformation, like Pokemons when they morph.
The idea is that I will have a monkey model and an elephant model, and I will make the monkey model glow from 0-1 and whilst I turn the monkey model transparency to 0 and sneakily switch to the elephant model and make it (de-)glow from 1-0. Voila the transformation. The problem is when I change the shader value (the shader for the glowing material), my monkey is fully transparent until the value hits 0.5 and then it will start showing up. There is no in between subtle glowing up or showing up, which is confusing...anyone got any suggestion?
It sounds like you probably have your material’s Blend Mode set to Alpha Clip:

The Alpha Clip blend mode is controlled by the Clip Threshold setting, which defaults to 0.5. This means that wherever your material’s opacity is below 0.5, it will render as fully transparent, and wherever it’s above 0.5, it will render as fully opaque. This clearly isn’t what you want.
Instead, you should change the Blend Mode setting to Alpha Blend. This will blend your object against objects behind it, giving you the smooth transition you’re looking for. You may also wish to disable the Show Backface option to ensure the whole mesh has a uniform transparency.