Subtle but noticeable effects

[Karzama]

Hi

I'm trying to find a way of subtling showing that a unit is upgraded, the idea is to be similar to TFT (a league of legends game mode) where the 2nd tier has silver parts on them and the 3rd tier has gold parts on them, I'm hoping to find something that could give units a bit of a glow without being too overpowering. But also still somewhat noticeable when other abilities and effects are being used.

Any ideas? Even something like a re-coloured pheonix fire effect could work?

 

[Devalut]

Sundering blades upgrade for knights literally adds a small effect to their weapons.

 

[Karzama]

Thanks I ended up settling for Barskin and Rejuvenation