Stealth

Stealth is the mechanic by which some units become invisible for a determined period of time.

Gameplay
Stealthed units will fade and/or disappear from enemy sight until they attack/have been attacked, or the duration of their invisibility effect expires. For some champions, using an ability that will cause them to become stealthed is preceded by a period called a "fade time", during which the champion appears partially transparent, but is still visible to enemies. During this fade time, any damage taken by the champion delays becoming invisible for a short period of time. No matter how many times a champion is hit, however, the fade time on invisibility cannot exceed five seconds. Summoner spells can be used during stealth without breaking it.

Items

 * Ward from
 * Ward from
 * Ward from

Champions
The main two stealth champions are and.
 * will stealth her until the Twilight Shroud ends or Akali steps outside of Twilight Shroud. Whenever Akali casts an ability or autoattacks inside of Twilight Shroud, she is revealed for 0.5 seconds. The Twilight Shroud also gives bonus armor and magic resistance for 10/20/30/40/50.
 * Evelynn stealths into the shadows only being seen by nearby enemy champions or true sight. While stealthed, Evelynn regenerates 1% of her maximum mana every second. Casting spells, taking damage or dealing damage reveals Evelynn for 8 seconds.
 * stealths her instantly for 0.5 seconds whenever she is brought below 40% health. When the stealth ends, she creates a clone of herself that deals no damage from autoattacks, and lasts for 8 seconds. This effect occurs almost instantly and can only work for once a minute.
 * will immediately stealth him for 3.5 seconds and teleport him in medium distance. Note that he blinks after stealthing, thus the enemy team cannot estimate direction he went without stealth detection.
 * will stealth him for 2.5 seconds and gives him 40% increased movement speed. If Talon breaks the stealth, The blades around Talon will converge and return to Talon, Dealing 120/190/260 damage to any unit they pass through.
 * will stealth him until he moves or attacks if stands still for 2 seconds. If Teemo breaks the stealth, he gains 40% bonus attack speed for 3 seconds.
 * allows him to enter stealth after 1.25 seconds of casting for 4/5/6/7/8 seconds. While stealthed, Twitch gains 20% movement speed. Upon exiting stealth, Twitch gains 30/40/50/60/70% bonus attack speed for 5 seconds.
 * gives her increased attack damage 25/40/55, a 1 second stealth after using and triple the bonus movement speed for.
 * will stealth him for 1.5 seconds and leaves an uncontrollable decoy that deals 70/115/160/205/250 magic damage after 1.5 seconds.

Invisibility detection
There are various ways for a champion to gain the ability to see invisibility. A champion with this ability will see invisible enemy units as partially translucent. When a revealed invisible unit leaves the revealed area that unit does not experience a fade time; the unit immediately turns invisible again. The following is a list of possible ways to detect invisible Champions:

Items

 * A Legendary Item whose active Covers an area with stealth-detecting mist for 6 seconds, granting vision of units which pass through it for 6 seconds. 60 second cooldown. (1000 Range, 375 AOE estimate). This item is only available in the Dominion game mode.
 * A consumable potion (400g) available at the item shop that grants invisibility detection to a champion until death. Any invisible enemies enter this champion's vision range while this potion is active will be revealed.
 * A consumable potion (250g) that was designed for the game mode Dominion. Available at the item shop that grants invisibility detection to a champion for 5 minutes or until death. Any invisible enemies that enter this champion's vision range while this potion is active will be revealed.
 * is a consumable item When placed on the ground these stationary wards reveal an area of the map for three minutes. Any invisible enemy units within their vision radius during this time will be revealed.

Champion abilities
The following abilities can reveal invisible units for a period of time:
 * , if her target stealths themselves during the channel
 * and
 * will provide semi-reveal. Though stealthed unit will still be immune to autoattacks and targeted spells, Duskbringer's trail will compromise position of said unit for 5 seconds, even through movement.
 * will reveal all enemy champions, wards and traps
 * will provide semi-reveal. Though stealthed unit will still be immune to autoattacks and targeted spells, Duskbringer's trail will compromise position of said unit for 5 seconds, even through movement.
 * will reveal all enemy champions, wards and traps

Presence detection without reveal
All abilities that do not require single target casting will affect stealthed champions but will not reveal them. These abilities can only be cast if an enemy is in range of the AoE casting circle, so when that ability is off cooldown, there is an enemy champion within the AoE.
 * can detect stealthed champions due to the particle effect pointing in their direction. The stealthed champion will not be revealed.
 * will explode but not reveal stealthed champions.
 * can detect stealthed champions due to the particle effect flying in their direction. The stealthed champion will not be revealed.
 * does not reveal stealthed champions but if they are within range and below half health, he will receive the movement speed bonus.
 * will explode but not reveal stealthed champions.
 * can detect stealthed champions due to the particle effect flying in their direction. The stealthed champion will not be revealed.
 * does not reveal stealthed champions but if they are within range and below half health, he will receive the movement speed bonus.
 * can detect stealthed champions due to the particle effect flying in their direction. The stealthed champion will not be revealed.
 * does not reveal stealthed champions but if they are within range and below half health, he will receive the movement speed bonus.

Skill shots
While skill shots that do damage and/or stun such as will still hit stealthed champions, they will still not be revealed. Note that the visible projectile will stop short of its trajectory and show visual and audio effects (eg. will make a splatter and show a small eruption of blood upon impact) if a stealthed unit is hit, indicating the stealthed champion's presence but not revealing them. Here are some more ways to detect stealthed enemies since they'll function the same as if they are unseen in brush.
 * will visibly entrap the stealthed champion without revealing the champion.
 * will visibly entrap the stealthed champion without revealing the champion.
 * can still missle lock on stealthed champions if hit with . You won't see the champion but you can see the debuff animation and follow it with your mouse.
 * Hook-type skillshots (,, and in some circumstances,  ) will show the effect of the hook happening without revealing the stealthed champion hit, revealing the champion's location.

Forcing enemies out of stealth
Taunting a stealthed enemy will cause him to attack, automatically revealing him and forcing him out of stealth. This can work if you target a visible stealthed unit or if the enemy is currently entering into stealth. With AoE taunts, such as or, this is easier as you can force every stealthed champion in the area to attack, even if they are invisible.

In the case of, skills which force him to move - such as , , , and knockbacks will also force him out of stealth.

Stealth Overhaul
A rework for the stealth system is currently planned by Riot. The goal of the rework is to create a non-binary stealth system: in the current system, a champion which can stealth himself for a long time in a non-limited area like and especially  is too powerful if the enemy team didn't buy an  or some s but too weak otherwise. This effect is particularly frustrating for new players who don't know how to counter stealth. Another weak point of the current system as stated by Riot is the ability for champions with long stealths to scout the map with no risks involved, granting their team a huge advantage in map awareness.

A rework has been put on hold while the stealth system gets changed. No date has been announced yet for the release of the new system.

It has been revealed that the current testing for the stealth overhaul will result in a permanent stealth state for and  once they put one point in the appropriate skill. From that point, they will remain in a stealth at all times and only be revealed when they perform an action (attack or use an ability). They will be revealed by stealth revealing as normal, but also when they approach enemy champions at a reduced distance than normal vision like. This will allow them to travel between lanes, past minion waves and s without detection but won't be able to walk around with the enemy team undetected anymore. Riot has stated that making stealth a weaker mechanic in general allows them, on the other hand, to buff and  in other aspects that were previously weak to counter-balance the potency of stealth.