We have a lot of character types in League, but one that I realized we don't really have is a thief. I'm talking about a get in, get out plunderer-type thief that is mostly unseen. Think the protagonists of games like Thief, Dishonored, or Styx.
The closest things we have currently have to this are:
Twitch: As far as lore goes (although, disclaimer: not a big lore person) he seems to fit this bill.
Twisted Fate: He seems like a good candidate to be this given his current passive, his background, and general feel of a sly guy.
Talon: Less thief and more an assassin, but still gives the feel if you were to play one of the aforementioned games as a high chaos/kill run.
Ivern: While he doesn't fit the thematic, the gameplay of stealing camps might satisfy this niche a bit.
Sylas: Steals ults, but doesn't fit with the grace or craft a thief might use. Besides calling it a steal, he really has no connection to this thematic in how he plays, looks, or in his story.
Zoe: Same as Sylas, except it's her W, not her R.
I think it would be pretty cool to have that feel of someone who goes around like a pickpocket. He would preferably have a camouflage and some ability that either works a bit like kleptomancy* or steals stats from an enemy temporarily (maybe even giving to an ally for the duration). He would be another assassin support as his focus wouldn't be damage per say, but he would play similar to an assassin. Although the idea is rather vague of what to do with this, I think there's a lot of potential for this, and I would especially love to see how CertainlyT would handle this.
**Different ideas for his thieving mechanics**
(Honestly just going to be a rambling/jumble of ideas from this point for said champion, because I'm bored and have nowhere else to put these ideas for now)
Maybe the twist is something like stealing camps that an enemy has recently injured gives extra xp and gold or something.
Or maybe something like he steals a tiny bit of xp and gold (say 1 each) per cs a nearby marked enemy kills (marked by damaging, lasts .75s as example, melee champ)
Where a champion, epic monster, large minion, or monster dies; for the next 30 seconds he can attempt to loot their corpse and receive an item from a specific pool based on what he looted. (Maybe include towers too).
Ex: A chance to get gold or XP based on level of enemy (with a multiplier based on what the enemy was: x1 minion, x2 monster, x4 champion, x6 epic monster), chance of small potion of iron from tower, chance of 1 time zzrot as trinket from herald/baron, chance of mini herald from baron (like size of canon minion with comparable significantly reduced stats, and slightly weaker charge), rare chance of rusty items from champs (picks up a completed item at random from a champ if he has room and gets to use for 60 seconds), chance of healing pots from minions and monsters, chance of elixers of wrath/sorceries from certain drags, chance of biscuits of rejuvenation from exploded poros (or scared ghost poros?), rare chance of one time use of keystone from champions, and chance of creating a zombie ward from them to name a few ideas/examples. (This ones my favorite so far).
Maybe a kit around stealing different aspects of people magically, in the sense that he controls them. For instance, Eye-jacking: blinds the target and gains vision around that target equal to their vision range. doing a small amount of base damage with a half decent scaling, but lasting for 1 to 2 seconds. Could probably do a few similar things, like a directed "charm" that could make them walk in a specified direction.
If I had to come up with a kit right now it would be:
P: Finders Keepers
Can loot deceased champions, neutral monsters, epic monsters, and large minions for 30 seconds after their death by channeling for 1 second. Chance of getting gold, xp, or an item based on the target.
Q: Purse Snatcher
Your next auto gains +50 range, deals X + Y (tAD) physical damage, stealing [10 - 20%] MS, and camouflaging you for [1.75 - 3] seconds after a 0.5 second delay.
Shoot a line skill shot dealing X + Y (bAD) + Z (AP) magic damage, blinding the enemy for [0.5 - 1.75] seconds and granting you vision around them for the duration of the blind. (1500 range).
Passive: Every third auto or damaging ability on an enemy champion will mark them. Damaging a marked champion will consume the mark, dealing X% + Y% (bAD) + Z% (AP) current health magic damage and granting 4 gold (half gold and damage if an ally breaks it). (Marks act like Vayne W in stacking/loss).
Active: Store up to [2/3/4] traps (based on level). Traps restock every X seconds. When someone steps on the trap they will become grounded for 0.25 seconds, after which the trap will detonate, rooting the champion closest to the center (that is still in the radius) for 1.5 seconds and grounding all others who are the radius for the duration the root lasts (no grounding if no root) and dealing X + Y (bAD) physical damage to the rooted target and half that to all others in the area upon detonation. (They're pitfall traps).
R: The Great Heist
Become untargetable for 0.5 seconds and gain [25/50/75] movement speed for 1.5 seconds. After 0.5 seconds deal X + Y (bAD) physical damage to all enemies within a 300 unit radius of you and gain the same (scalings) as max health per enemy hit for 2 seconds.
As a basic backstory idea: Was an impoverished teen in Bilgewater trying to get by as a pickpocket when he steals from the wrong person and has to run for his life only to find out he can use magic to manipulate his pursuers into killing each other. Then loots their bodies and heads home after.