The below is a complete rework. Shaco has been reclassified as a Duelist / Rogue. Compared to other Duelists who have to adopt an assassin playstyle or boycott large fights entirely, Shaco's kit affords him relative safety on the front line. His damage-output and area of effect presence continually ramps up unless enemies specifically spare resources to deal with him, which is tied into his damage-mitigation mechanic (that is a staple of duelists).
Shaco, the Mad Jester
How about a magic trick?
Every third consecutive attack against the same target will summon a hallucination of Shaco that continues to attack his target. Each additional Shaco/Hallucination attacking an individual target will deal 50% less damage than the last, for up to 200% damage from ∞ Shacos.
Hallucinations from any source will be dismissed instantly if they take single-target/targeted-AOE damage from an enemy champion or turret, or if Shaco goes more than 3.5 seconds without landing a basic attack or casting an ability.
Hallucinations summoned by Hallucinate will disappear in a poof once their target has died.
Shaco and his hallucination will appear in a puff of smoke that conceals which Shaco is the original, with which side Shaco appearing on being decided at random.
Active: Shaco blinks to the target location and arrives with a hallucination. This hallucination will follow Shaco around and attack whom he attacks.
Ideally, this hallucination would walk side-by-side with Shaco - perhaps even fully controllable by the summoner (obeying the same inputs as Shaco).
Active: Shaco has all hallucinations in an area under his cursor explode in a fanfare of horrors, dealing magic damage to surrounding enemies and causing them to flee for a few seconds. Each additional explosion versus an individual enemy deals 50% less damage than the last.
Active: Shaco has all his hallucinations and disguised allies hurl a dagger toward the target location, dealing physical damage to enemies hit. Each additional dagger versus an individual target will deal 50% less damage than the last.
Active: ACTIVE: Shaco throws down a smoke bomb that obscures enemy vision over the surrounding area for 0.75 seconds, disguising all allied champions touched to resemble Shaco and gain Hallucinate for a few seconds. The disguise is removed if a champion takes multiple sources of single-target/targeted-AOE damage. Enemy champions within the smoke are blinded.
Disguise Duration: 3.5 / 5 / 6.5
Dismiss Requirement: 2 / 3 / 5
Cooldown: 100 / 90 / 80 seconds
Due to the relative lack of animations within his own abilities, Shaco will instead have a relatively large amount of animation support for his Mirror Images - dashes, channelled spells, empowered attacks, etc.
Ranged Disguises will hurl their dagger on each attack.
Hallucinations spawned by disguises will be a copy of Shaco, not the disguised champion.
Hallucinations will ignore Shaco's de-spawn conditions so long as their ally is disguised (i.e. if he's out of combat, the hallucinations won't instantly despawn.
Blind now reduces the target's vision radius and removes their allied vision for the duration. Minions and monsters will continue to miss their attacks.