By killing a champion that currently possesses this buff, the buff is then passed to the killer. In this case, the duration of the buff is refreshed.
After an allied Ivern (higher than level 5) applied and consumed Friend of the Forest on the camp, by walking within the camp area.
Re-applying the debuff the moment the target is dealt damage from it may cause the target to get dealt the damage of 2 ticks.
Re-applying the debuff and triggering Electrocute may cause the target to get dealt the damage of 3 ticks, with 1 tick dealing 40 true damage.
The buff is only lost on time-out or death by enemy champion; executions will not lose you the buff.
The slow is more effective when applied by melee attacks than ranged attacks. Note however that it is easier for ranged champions to apply the slow without getting in dangerous situations and they can also use it to keep melee attackers at a distance.
The jungler will most likely take the red buff early in the game.
The extra damage lets the jungler clear minion packs easier and take on bigger monsters like the Dragon.
The slow from the buff is extremely valuable for the jungler to successfully execute a gank and is also useful for kiting monsters to reduce damage.