Stuff like:

shielding cooldown
shielding duration
Shielding invulnerable yes or no. (if not invulnerable they're just incredibly resistant, so they can still be knocked back or kept away/CC'd/disabled in other ways. not just completely unassailable.)

Also, it could be neat to look into a similar special effect for shielding being similar to the orbiting shields that the "relics" mod uses for it's reflection necklace so that it's more visible and obvious

Also potentially rework it so that it defends the entity from a set number of hits but it requires being hit before powering off, so it's a temporary defense against strikes which you need to try to land while dodging them in their invulnerable state.

https://www.youtube.com/watch?v=uY6FljzyihQ
a video of a fight being very drawn out by a very stacked and cunning enderman. :V