The Rift Herald is a powerful neutral monster that can be found in Summoner's Rift, in the same pit as Baron Nashor. She uses basic attacks and abilities to fight her foes.
Slaying the Rift Herald drops the Eye of the Herald at the entrance of the pit, which grants Empowered Recall and the ability to summon the Rift Herald to push a lane. The Eye of the Herald can be picked up by one member of the slayer's team and despawns 20 seconds after it drops.
The Rift Herald spawns up to two times per game. It despawns permanently at 19:45, or 19:55 if in combat. The second Rift Herald only spawns if the first one is killed before 13:45. If the first Rift Herald is killed when the timer shows exactly 13:44, the second Rift Herald will spawn at 19:45 and instantly despawn. Baron Nashor spawns in the same position at 20:00.
Scuttler Crabs or Rift Scuttlers live in the fresh waters of Valoran and can be found near the docks of Bilgewater and in Summoner's Rift. They are small green-shelled crustaceans with 3 pairs of legs and one pair of front claws. They sometimes bury themselves into the muck of the river to avoid predators and are known to either avoid or flee from dangers. To confer peaceful resolution (hence the elusive pacifist nickname) to the force that subdues it, it will grant them a boon: a persistent field around it that grants vision and magical speed to the aggressor and its allies. If corrupted by The Void, a Rift Scuttler turns into a Rift Herald.
The level of the Rift Herald is the average of the levels players have when it spawns, with a minimum of level 6.
The Rift Herald's basic attacks deal (4% of target's current health)bonus physical damage.
Monstrous Toughness: Effects that deal damage based on Rift Herald's health and are not usually capped, are capped at 50 damage.
Warped Armor:Rift Herald's is immune to all disabling debuffs.
The Eye of Baron:Rift Herald has a vulnerable eye on her back, which makes champion basic attacks against it deal (12% of Rift Herald'smaximum health)bonus true damage. When the eye is hit, it closes for 10 seconds, reduced by 2.5 seconds every time she is struck by a champion's basic attack. The eye doesn't open more than once every 3 seconds or if the Rift Herald is below 15% maximum health.
Charge: At the start of the fight, the Rift Herald winds up and charges forward, knocking aside enemies she passes through and damaging them for 200% AD.
Swipe: At 65.75% and 32.75% of Rift Herald'smaximum health, it winds up for an attack that deals 300% AD in a cone in front of her.
The Eye of the Herald can be crushed to summon the Rift Herald. The summoned Rift Herald relentlessly pushes her way to the enemy Nexus. The summoned Rift Herald has different statistics, effects and abilities than the pit Rift Herald:
It heads to the closest lane and start pushing it.
It focuses mainly on the closest minions and structures. It only targets champions if they attack it first.
Its level is the average of the levels of the champions of both teams the moment the Eye is picked up.
It is summoned in champion facing-direction (not dependent on cursor).
Its basic attacks deal 1.75% of Herald'scurrent healthbonus physical damage.
The Eye of Baron: Every 3 seconds, the eye on Rift Herald's back will open. Champion basic attacks against the eye deal (40% of Rift Herald'smaximum health)bonus true damage.
Leap Attack: When the Rift Herald approaches a structure, she winds up for a few seconds and leaps into melee range, dealing 2000 − 2750 (based on level)true damage to the structure, 200% AD physical damage to nearby champions and 66% of Herald'scurrent health true damage to itself.
Enrage: At 65.75% and 32.75% of Rift Herald'smaximum health, it winds up for an attack that deals 200% AD in a cone in front of it.
Duchess Smash: It disables turret backdoor defenses even when no minions are nearby.
Attacking the Rift Herald's Eye is considered as an on-attack effect and will benefit from the player's spell vamp.
The summoned Rift Herald has a hefty amount of health and damage and several skills focused on taking down towers. If left unchecked, the Rift Herald can rapidly destroy multiple towers.
Since a summoned Rift Herald prioritizes minions and structures, it is not possible to distract it from smashing towers. The only way to stop the Rift Herald is to take it down.
Rift Herald will dance if a champion dances nearby, or if she is alive and near the enemy Nexus when it is destroyed.
Rift Herald's charge attacks against towers or other structures can be blocked by Champions if they stand between the Rift Herald and the attacked structure. This causes the charge attack to deal very little damage against the initial target but instead damages the blocking champion.
If the Rift Herald is in range of two structures and winds up to charge at a structure that gets destroyed before she starts to charge, she will charge to the next available structure instead from the same wind-up. 
In patch V7.9, it was stated that Rift Heralds were exclusively female.
From patch V5.22 to patch V7.9, the Rift Herald looked like this:
Bug Fix: Fixed a bug where canceling Eye of the Herald's summoning ritual at the very end of its 0.25 seconds wind-up (before the uncancellable 3-second channel begins) could cause the item to go on an extremely long cooldown, preventing it from being used before it expires.
New Effect: Rift Herald is captured in the Eye of the Herald when killed. Any member of the team that killed Rift Herald can pick it up, temporarily replacing their trinket. Eye of the Herald grants Empowered Recall while held and expires after 4 minutes if not used. Channeling Eye of the Herald for 3.5 seconds will crush it to summon Rift Herald from the void as your team's ally.
Has 4000 - 6400 health, 425 movement speed, 80 - 200 attack damage.
Basic attacks deal 3% of Herald's current healthbonus damage, in addition to base AD.
When Rift Herald approaches turrets she winds up and leaps into melee range, dealing 150 damage (+ 25% of her current health) to the turret and herself.
Eye opens every 3 seconds.
Poking Rift Herald's eye deals 20% of her maximum health as damage.
Rift Herald can be affected by most forms of crowd control.
Rift Herald disables turret backdoor defenses even when no allied minions are nearby.
While there are no allies nearby, you take 5% damage reduction from enemy champions and generate X / Y (based on level) Corruption stacks per second. At 100 stacks, your next basic attack consumes all stacks to deal 15 / 270 (based on level) bonus magic damage. Works versus structures, damage halved for ranged champions.
Lasts for 20 minutes and is retained even if slain.