Crowd Control Diminishing Returns also known as CC DR is a system that will reduce the effect of stuns, root, and incapacitation effects in PVP when a target has been affected by them several times in a row.
Spells are categorized into three groups. All spells within a group will affect each other and trigger a DR reduction if they are applied to the same target within a 15-second window after the effect has ended.
Stun: Charge , Mage freeze ( only the stun part )
Root: Chilling Radiance
Incapacitate: Agonize , Taunt
DR timers last for the duration of the effect plus 15 seconds. If an effect of that category is applied within that timeframe, the DR window will be increased, and the duration of that effect will be reduced by:
2nd application: 50%
3rd application: 75%
4th application: 100% (immune)
After the 4th application, where the target is immune, the DR window will no longer be extended and the target will return to DR level 0 for that category at the end of the DR duration.
This is only active in PVP, and on Wardens and Kings, but not on regular Monsters.