A small Twitch buff
Twitch is a champion who has been completely underplayed since the patch after his visual update, where Riot gutted pretty much everything that made him good as a champion. I feel like some buffs wouldn't be awful for making the Plague Rat at least able to keep up with the strong picks. These changes aren't huge, just enough to make him viable without enough to make him broken.
Q-Ambush: Twitch's stealth got pretty heavily gutted, making it only useful as either a very early escape or as an engage. Its delay goes up to 6 seconds at the most if he's getting hit while the delay is ticking, and just having a delay is weaker than some champions (looking at you, Shaco.) With the state of vision in the game when the change was made, it was honestly justified and a pretty decent change. But at this point in the game, the vision game has been completely reworked and this change is made near obsolete with an Oracle's Alteration and enough skill shots. Reverting the stealth back to how it originally was, with no extra delay if he's taking damage, or at least a shorter extra delay if he's taking damage, would help him get out of sticky situations and not drop his cheese on the way out.
W-Venom Cask Venom Cask is, right now, only used for the poison stacks and the slow. It deals no real damage, so you just throw a point into it at level 3 and then forget it exists for a while while you max your stealth and your burst first. I feel like Twitch players should have a bit more incentive to give W some points over Q, so I'm thinking make the number of stacks it gives 1/1/2/2/3, based on rank. This will hit his early game a little bit but buff him once he gets to his late game. I would say throw some real damage on it instead of this, but to be honest I don't think either of those changes would really happen. Giving it damage, even low damage, would make his early game very strong.
So, those are the changes I feel like Twitch needs. He has, last I looked, a 51% win rate and dropping as people start picking him more. YouTubers like Phylol and Jeremy Gaming Curios have been saying he's pretty strong, so people who watch them are picking him up and trying him out. Problem is, none of these guys have any idea what to do with him, so his win rate is plummeting as his play rate rises. When I looked a week ago, his play rate was 3.6% and his win rate was 55%. That's a pretty heavy drop in win rate for such a small play rate increase.