An idea of showing Scorpion's undeadness could be similar to this Pirates of the Caribbean scene.

Here

In this scene, due to the curse, moonlight reveals what they really look like. It's dated sure, but a good visual.

For this idea to apply for Scorpion, what about whenever hell fire is summoned a revealing undead effect like that happens. Applying to any of Scorp's combos, specials and finishers like Toasty.

During these short moments of hell fire, Scorp's entire look changes. For example the traditional yellow garbs become torn and faded like what he was buried in. Everything flashes as a negative undead version in this moment.