Successive stuns on the same target within a 60-second window grant the target "diminishing returns", cutting the duration of each subsequent stun in half (rounded down). For a normal 6-second stun ability, the durations are 6s, 3s, 1s, 0s, ...
Diminishing returns expires sixty seconds after the START of the last succesful stun, and applies even if different players perform the stuns. There is no buff/debuff indicating that diminishing returns is in effect.
