Let's say I wanted a skill to lose its effectiveness over time. Specifically, its stun effect should apply 100% of the times on first use, then 70% of the times on second use, then 40, then 10... You get the idea.
Is there a way to achieve this per enemy? A way to give them additional resistance to stun with each use, for example? Or any other way you can think of to emulate such behaviour in practice?