Disclaimer, I'm Silver IV if that's relevant. I've been playing Shaco since the beginning of Season 3. If you find anything I say to be incredulous, ridiculous, or truly, truly (truly?) outrageous, consider it exaggeration for narrative effect. Also, TL;DR at the bottom.
I'm convinced that Shaco should be a support. Not only that, Shaco should be the League's premier support assassin. Hear me out. Shaco is currently identified as, and primarily played as, an assassin. His kit is great for it, no doubt. His kit is also great for the support role in a lot of interesting ways, and as I'll argue, so are his narrative and theme. If Riot, through some miracle, came to view Shaco through such a lens, they might find a more compelling, unique character - perhaps, even, a soul - for our beloved Demon Jester.
But first, a little history. Ages ago Shaco was considered ban worthy. His ganks were oppressive, his damage ludicrous, his mobility unparalleled. He was legendary, for a brief time, as the most toxic thing in League. Anti-Fun. Simultaneously unfair and over-powered. (Zileas - On Shaco) Riot, seeing the monster they had created did the only sensible thing - they nerfed him. The nerf was, however, merely number and ratio changes. His functionaility didn't really change. They took his strength, but left what made him frustrating.
So he goes untouched for one season, then another, then another. During this time he becomes notorious for being a 'feast or famine' champion, an item dependant, unimpressive team-fighter, that can ambush and split-push with the best of them, but is more often than not a liability. (Xelnath - On Shaco) A nuisance. A champion that you don't want on your team and you don't want to see on the enemy team. Either unstoppable or laughable. Maybe that's appropriate.
Yet he has one saving grace: the counterplay inherent to his kit is near zero while granting him the potential to outplay his opponents. (Xypherous - On Shaco) He doesn't require high mechanical skill, just in-game knowledge and good positioning and timing to abuse his tricks. Its the reason you still occasionally encounter those god-like Shacos. So he endured, purposefully under-tuned with questionable utility but not utterly impotent.
Now it's almost 2016. Taric, Poppy, Warwick, maybe even Urgot, are due for an update. How many champions left before Riot decides to tackle Shaco? Some have been so brave as to post how they think Shaco should be reworked. They scare me. Their solutions are many, and varied, and range from complete kit overhaul to what amounts to nerfs to what are obviously buffs. Rarely is their any compensation or consideration for the enemy against Shaco. The poor fools.
"What if we made his Backstab do % health damage? Or maybe true damage?! He definitely needs a reset on his Q when he kills someone. And movement speed. Don't forget making boxes spring faster, scale better, and debuff the opponent. His ult needs to copy all of his buffs and be able to explode on command and be controllable after his death and mimic all his spell casts. Oh, and his E-"
And his E. Indeed. If Riot were to humor us and grant us the Shaco rework many seem to want, we'd have another Rengar. Or Kha'Zix. Or Talon. Or Zed. He'd be pushed into the role of a squishy assassin permanently, with one definitive build path, one particular pattern with which he can effectively and efficiently delete an enemy squishy. (@Riot: The Real Tragedy of Shaco) Fun? Maybe. Balanced? Maybe. Would it still be Shaco? I doubt it. There is some hope, though. Riot hesitates. Why? I think, perhaps fittingly, it's a crisis of identity.
I said Shaco should be a support. It's important to phrase it precisely this way. Should be. Similiar to how Sion was an AP burst mage, (who could build straight AD with lifesteal if he was feeling daring) before Riot took a long, hard look at what he should be. Morello talks a lot about how champion design is informed by a particular fantasy, and the more you dial into that fantasy through their thematic and kit design, the more interesting and coherent that champion will become. (@Morello: On The Tragedy of Shaco) So what is Shaco's fantasy?
Well, the League community seems to see Shaco as the homicidal slasher, the psychotic killer, the Batman's Joker with extra chaotic-evil clown thrown in. In short, they see the Demon. But where is the Jester in all of this? Where is that sly devil who watches the drama unfolding before him, the only one aware they're all on stage? Who sees the pieces moving around the board but has no stake in the winners or losers, and finds it entertaining nonetheless? Who is instrumental to the story, though he is not a main character, remaining in the action but apart from it?
Jesters historically have always been subservient to their liege, albeit in a subtle and subversive way. Is such a role unfitting for Shaco? There are so many notable figures in the League: great kings, queens, generals, nobles, and aristocrats. Many of these guys and gals are your hard carries, your renowned fighters, your arch-mages. These champions are easily the stars of League of Legends. Let them keep the spot-light. Shaco doesn't need it. He doesn't want it. Shaco works behind the scenes, setting things in motion, pulling the strings. I can't help but think that, with all the events that could / will / do occur lore-wise, Shaco has a small part in everything. He probably knows a great many secrets about his fellow champions, their world, and more, but having no allegiance to any one faction or another he prefers not to tell. Besides, that would ruin the fun - his fun.
The juxtaposition of having a creature as unsettling and malfeasant as Shaco also be the one you must trust, whether you believe him or not, compliments the paradoxical nature of him being the support assassin - the Demon Jester. It places him in a unique position, one that suits him, in my eyes, and enhances his already distinctive flavor.
Perhaps most importantly, Shaco strikes me as the symbolic Fool. In the Tarot, the Fool occupies an interesting space, simultaneously having the lowest value and the highest (making him the trump or wild card) depending on context. In art he is often seen as blissfully unaware, teetering on the edge of a precipice. Shaco goes a step further, and having crossed that threshold, fails to make the transition from ignorance to enlightenment and falls into madness as a result. But it isn't just insanity. It seems almost like a sinister prescience. Shaco knows. While he can be unpredictable to his enemies everything he does is deliberate. Others can't comprehend him because they don't see the bigger picture, the larger forces at work. They search for answers and meaning and struggle to make sense of it all. Shaco just laughs at them. Their mistake is in thinking that they're playing the same game.
"An assassin is an agile champion that specializes in killing or disabling high value targets. Focused on infiltration, deception, and mobility, assassins are opportunistic hunters who find favorable moments within a fight before jumping into the fray. Regardless of the size of the enemy team, assassins specialize in positioning and artful killing. They strike when the time is right – no sooner, no later." (LoL Wiki - Assassins)
"Supports make plays by enabling their allies through buffs and heals, or by disrupting enemy lines through crowd control. From laning to late game teamfights, supports create advantages and opportunities for their teammates to capitalize on. A skilled support gives their team the edge it needs to claim victory, and can turn the tide of battle with just one well-timed play." (LoL Wiki - Supports)
Are these two champion roles mutually exclusive? I don't think so. Shaco fits both amazingly. In this video, Riot PAX East 2015 - The Journey of Champion Design, the Rioter CertainlyT, recounts the story of how he looked at Thresh as a fighter operating from the jungle, before Zileas (VP of Game Design) suggested (offhandedly) making him a support. CT initially couldn't see it, but realized he had been blinded by his preconceptions and that part of the the evolution a champion is having other people's insights inform you as to who a champion is and who they could be. Now it seems almost impossible to see Thresh as anything else. He is an excellent support, certainly, but what exactly about a sadistic wraith thematically identifies Thresh as such? His mechanics fit, yes, but where is the flavor?
Shaco's kit, even as it currently stands, lends itself to the support role. His Q lets him escape situations that would be disastrous for other supports and scout and roam effectively. His E, with its permaslow, lets him chase and peel all but the most tenacious enemies, while his passive punishes those who ignore him as they try to reach Shaco's allies. His ultimate nearly doubles the effectiveness of all of these things. And with his boxes, Shaco is simply the best champion at warding in the game, can leash like no other, and foils most gank attempts. (Supporting As Shaco - Unconventional But Effective)
He already has the scalings of a support, all he needs are QoL utility buffs and bug-fixes. I also want to see Shaco have some real counterplay for his opponent and the tools to outplay them in turn. Shaco, of all champs, would be the one to play with his victims. Very minor changes would need to be made to make Shaco more suitable in lane with a duo partner and still preserve his ability to jungle. I think it's crucial that he has both these dimensions to his character. I also think making him a support neatly answers the question, "What is it that Shaco should be doing (and that Shaco players want to do) in the late game that makes them and their teammates feel good about having him on the team?" (RiotRepertoir - On Workshop Shaco's Proposal) My answer would be, he's responsible for map control, peeling, zoning, disengaging, chasing, and sieging, all while still being able to get picks if he sees the opportunity.
Shaco, built with moderate tankiness and utility, can can act like a 'dodge-tank', easily aggro'ing the enemy opening them up to punishment from your allies. He takes the hits, not because he's tough-as-nails, but because he's this unflinching punching-bag that just keeps smiling, always smiling. He's also great at running interference and buying time for his teammates to make a hasty retreat or get the last few hits on that objective. The "jack-of-all-trades" approach is also core to what it means to be Shaco. Because there is no one optimal build, Shaco has the flexibility to be whatever his team needs him to be. (A New Way Of Thinking About Shaco)
For those of you interested in how Shaco could be (and should be, IMO) updated to fit more inline with the support role, you can check out my proposed Shaco Season 6 Update.
If you read all of this, you have my thanks and admiration. I will be editing / formatting it further for clarity, but I'll have to leave it as is for now. If you disagree, or find my argument wanting, let me know and please explain why. I hope I've been coherent and cogent for the most part.
And if you think all this is crazy, that this would destroy Shaco and the League of Legends, remember: sometimes a little chaos is in order. ;)
TL;DR: Shaco is actually a support, Riot just doesn't realize it yet.