Invisibility

Overview

In World of Warcraft, invisibility can mean a couple of things:

1. A power or spell to render something unseen or hard to see similar to [Stealth], but usually with some magical cause.
2. An ability of the Warlock's Succubus pet taught by the  [Grimoire of Lesser Invisibility].
3. A specific Mage spell that was removed from the game for balance reasons but is being reintroduced into BC, see Mage Spell section below for more info.

Details

Invisibility in World of Warcraft comes in three grades: Lesser Invisibility, Invisibility and Greater Invisibility. The only difference between the grades is in terms of what grade of detection magic works against them.

Invisibility Detection

There are items and spells in the game that provide the ability to see invisible beings. Just like invisibility itself, these detection effects have three grades: Lesser Invisibility Detection, Invisibility Detection and Greater Invisibility Detection. The grade determines what rank of invisibility can be seen. For example, an Invisibility Detection effect can allow someone to see targets with Lesser Invisibility and plain Invisibility, but targets with Greater Invisibility will remain undetected; a Lesser Invisibility Detection effect would detect only Lesser Invisibility.

Unlike [Stealth], there is no chance to detect an invisible target without a high enough grade of detection magic, but on the other hand, if the detection effect is of sufficiently high grade, the target has no chance to remain hidden.

Items that provide invisibility detection include (Thottbot links): Elixir of Detect Lesser Invisibility (requires level 29 to use; lasts 10 minutes).

Spells that provide invisibility detection include the Warlock spells Detect Lesser Invisibility (acquired at level 26), Detect Invisibility (level 38) and Detect Greater Invisibility (level 50). These buffs can be cast on any ally, not just the Warlock, and last 10 minutes. They do have a minimum level requirement for the target, however; I suspect it is the same level that enemies would have to be to yield experience or honor for a Warlock whose level was just high enough to cast the spell.

Using Invisibility

There are only a few items in the game that provide any grade of invisibility. They are: Lesser Invisibility Potion (requires level 23 to use; lasts 15 seconds with a 10-minute cooldown), Invisibility Potion (requires level 37 to use; lasts 18 seconds with a 10-minute cooldown), and Gnomish Cloaking Device (requires 200 Engineering to use; lasts 10 seconds with a 1-hour cooldown).

Just like Stealth, invisibility comes undone if you take most actions other than movement; unlike Stealth, however, your movement speed is unaffected. However, if you take any damage or receive any healing while invisible, the effect is gone immediately; do not bother to use invisibility if you are currently affected by a DoT or HoT effect.

Invisible Mobs

There are a several invisible mobs in the world. There are the ghosts in the Ruins of Lordaeron in Tirisfal Glades, the ghosts in Raven Hill in Duskwood, and the infamous invisible patrols in Dire Maul West.

Then there are the dangerous Elite Ambushers in the Silithus Hive Ashi and Hive Zora, the Eyeless Watchers in the 3 main encampments in the Eastern Plaguelands and of course the Stratholme Eye of Naxxramas (as soon as you hear this last one yell "The Living Are Here!" kill it immediately or it will summon 2 elite bats).

Other than the Dire Maul, Silithus and Eastern Plagueland ones, however, the most invisible mobs of the world tend to be neutral, and won't attack unless provoked, which means that you wouldn't know they were there unless you had invisibility detection magic. At this time I know that the Raven Hill ghosts possess a regular Invisibility effect (neither Lesser nor Greater), and suspect that the others have the same.

Mobs with Invisibility Detection

Each of the major cities has patrolling guards with Stealth and invisibility detection abilities, and some mobs in instances (some were added to Stratholme in patch 1.6, for example) can also detect some grade of invisibility. Exactly what grade they can detect, however, I don't know at this time.

Succubus Power

The Warlock Succubus pet can be taught Lesser Invisibility through a Grimoire of Lesser Invisibility, obtained at a Demon Trainer and usable by the warlock at level 32. The spell costs the Succubus 100 Mana and is especially useful in pvp or to bypass mobs in a dungeon. Usable only out of combat, Instant Cast, duration of 5 minutes.

Mage Spell

Invisibility - Rank 1

Requires Level 68

263 Mana

Instant cast

5 min cooldown

Fades the caster to invisibility over 8 sec. The effect is cancelled if you perform or receive any hostile actions. While invisible, you can only see other invisible targets and those who can see invisible. Lasts 20 sec.

from [1]

Tables of Invisibility and Detection

Template:Bc

Invisibility Level	Duration	Source
100	5 min	Template:Class Icon Warlock SmallSuccubus' Lesser Invisibility
100	15 sec	Template:Lcommon
200	10 sec	Template:Lcommon
200	18 sec	Template:Lcommon
200	5 min	Template:Luncommon
340	20 sec	BC Template:Class Icon Mage SmallInvisibility
Detection Level	Duration	Source
50	Equip	BC Template:Lrare
100	10 min	Template:Lcommon
100	10 min	Pre-BC Template:Class Icon Warlock SmallDetect Lesser Invisibility
200	10 min	Pre-BC Template:Class Icon Warlock SmallDetect Invisibility
300	10 min	Pre-BC Template:Class Icon Warlock SmallDetect Greater Invisibility
1000	20 sec	BC Template:Class Icon Mage SmallInvisibility
1000	10 min	BC Template:Class Icon Warlock SmallDetect Invisibility