Crusader Kings II

[Chaotix]

If you're at 100% decadence, you will sooner or later get hit with a Decadence Invasion.

Some county will revolt and come at you with roughly as many troops as you can muster in your entire realm. And they're all attrition free.

You'll also lose 50% decadence. But as soon as it jumps back up, you're susceptible to getting another one.

The way I handled decadence the last time I played Muslims was by keeping my dynasty very small. I was playing as Rum, so it eventually meant assassinating all of my Seljuk cousins. I also revoked or killed all of my vassal relatives and kept only my desmesne under Seljuk rule. Then give your designated heir a county and imprison the rest after he inherits. Rinse/repeat. With such a small dynasty you rarely gain any decadence, though it can be dangerous not knowing whether you'll have an heir.