Current wording:
EMBOLDEN:
Increases own magic damage by 10% and physical damage by party members by 10%.
Both effects are reduced by 20% ever 4 seconds.

At first I was like "HUH, will this actually nerf my damage after 4 seconds ?" then I saw how it worked ...

Rewording suggestion:

EMBOLDEN:
Grants 5 Embolden stacks to you and party members in range.
Each stack increases your magic damage by 2%, and each other party member's physical damage by 2%. One stack is lost every 4 seconds.