Illusion magic is another thing I think ESO is sorely missing so I've been brainstorming a skill line that could be added without violently unbalancing the game (at least more so than it already is)

Firstly, a few new status effects would need to be added.

Pacify (NPC) - Target will behave as if no enemy is present (broken by damage).

Pacify (player) - Target cannot attack or cast hostile spells (broken by damage).

Frenzy (NPC) - target runs to and attacks its nearest ally.

Frenzy (player) - 100% of target's outgoing single target damage is redirected to its nearest ally.

--Active--

Clairvoyance - Increases stealth detection range by 25/30/35/40% for 20 seconds.

Foresight - Increases stealth detection range by 50% and grants 10/12/14/16% increased damage against stealthed enemies for 20 seconds.

Enduring Clairvoyance - Increases stealth detection range by 50% for 24/26/28/30 seconds.


Calm - Inflicts pacify on an enemy for 2/4/6/8 seconds.

Pacification - Inflicts pacify on an enemy for 10/12/14/16 seconds.

Harmony - Inflicts pacify on up to 5 enemies in the target area for 10 seconds. If the pacify breaks from damage, the target is silenced for 2/3/4/5 seconds.


Muffle - Decrease your stealth radius by 1/1.5/2/2.5m for 10 seconds.

Silent Stride - Decrease your stealth radius by 3m and gain minor expedition for 10/12/14/16 seconds.

Silent Stalker - Decrease your stealth radius by 3m and increased sneak attack damage by 7/8/9/10% for 10 seconds


Fear - Inflict fear on an enemy for 2/2.5/3/3.5 seconds.

Rout - Inflict fear on an enemy for 4/4.5/5/6 seconds.

Hysteria - Inflict fear on up to 3 enemies for 4 seconds in the targeted area. When the fear ends, the targets are inflicted with blind for an additional 2/3/4/5 seconds.


Invisibility - Become invisible for 1/1.5/2/2.5 seconds.

Swift Shadow - Become invisible for 2.5 seconds and gain major expedition for 3/4/5/6 seconds.

Ghostly stalker - Become invisible for 2.5 seconds and gain empower for 3/4/5/6 seconds.


--Ultimate--

Fury - Inflict frenzy on an enemy for 6/7/8/9 seconds.

Mayhem - Inflict frenzy on up to 5 enemies in the targeted area for 10 seconds. After the frenzy ends, the targets are exhausted and inflicted with minor maim for 7/8/9/10 seconds.

Unending Fury - Inflict frenzy on an enemy for 10/11/12/13 seconds. If the target kills one of its allies while frenzied, the duration is refreshed.


--Passive--

Sanguine Gaze - Increase health recovery by 1/2% for each target affected by your illusion spells.

Aspect of Terror - Enemies effected by your fear spells have their movement speed reduced by 15/30%

Light Foot - Increases stealth movement speed by 10/20% while an illusion spell is equipped.

Illusion Mastery - Reduces the magicka cost of illusion spells by 10/15%

Master of the Mind - Increases the duration of Illusion spells by 1/2% for each illusion spell equipped.

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I look forward to your feedback.