Diminishing returns means that certain spells and abilities become less effective against a target if used frequently within a short period of time. While diminishing returns mostly applies to player characters, some abilities also have diminishing returns in PvE. The table below contains a list of abilities that are affected by DR, and under what circumstances. In addition, DR categories are listed. Effects within the same category share diminishing returns.
When an ability with diminishing returns is used against a target in PvP, the first effect has full PvP duration. If the same category of effect (e.g. root) is used on that target within 18 seconds, that effect's duration is reduced by 50%. On the third use, the duration is reduced by 75%. After this, the target is immune from all effects in that category for the next 18 seconds. Note that when used against another player, effects will only last for their PvP duration, often far shorter than the duration stated in the ability's tooltip. The maximum PvP duration is 8 seconds.
Spells must be used on the same target within 18 seconds of the * end* of the duration in order to be diminished. In other words, if a target hasn't had a root spell active on them for more than 18 seconds, this category of diminishing returns will be reset on the target, and the next rooting spell will have full effect.
This is hot it works in World of Warcraft, DBO should use a system like that too or you may stuck in CC (crowd control) chains for years.
