Looks like you colored this green instead of red.
But seriously, in what world is this Pokemon fine in? More so than some of the other Pokemon in Yellow and Red.
First and foremost, this mon is practically impossible to revenge kill without incredibly strong priority. Like, it can survive Tera Normal E-speed from Choice Band Dragonite.
252+ Atk Choice Band Tera Normal Dragonite Extreme Speed vs. +1 0 HP / 4 Def Grassy Seed Sneasler: 220-261 (73 - 86.7%) -- guaranteed 2HKO after Grassy Terrain recovery
Unless you're using Talonflame, most priority requires significant chip damage.
The only other option besides priority that is incredibly strong is Barraskewda in Rain specifically, and Regieleki with Scarf specifically, and that is fucking Adamant Sneasler too. If the DLC gives us Ninjask and Accelgor, it'll be only other 2 Pokemon that can outspeed Sneasler. Ditto is unable to because transform does not copy Unburden boosts, so you're left with just priority (from something with +1 Def or Psychic Terrain up), and 4 whole Pokemon, 2 of which need a certain field condition and 2 that are already fast Pokemon who need Scarf.
Second, unlike other Unburden sweepers with such high Speed like Accelgor, Sceptile, and even Hawlucha, none of them are even remotely as strong as Sneasler and have almost no defensive counterplay. It beats out Hitmonlee as strongest Unburden user while also having dual STABs that compliment one another, Sword Dance, and of course hax. Looking at the Honkalculate;
-Only Gholdengo, Landorus-T (bulky variants), Dondozo, Skeledirge, and barely Clodsire survive more than 2 hits at +2
-Swap Gholdengo/Landorus-T for Gliscor/Okidogi if Sneasler is using Lash Out
-Only the Unawaremons can switch into Sneasler in both accounts
Keep in mind, Grassy Terrain is almost certainly up, so Clodsire only deals 50% at most before Sneasler heals and Gliscor doesn't even 2HKO. This is also WITHOUT Tera as well. Even without extra STAB or super STAB, it starts OHKOing vast majority of things with very little effort late game. Granted, with Tera Sneasler actually has more counterplay and honestly weaker because anything can become Poison or Ghost (not really a point for it, but Tera in general people overlook). Once Sneasler gets in with 1 turn to set up (which is really easy because Rillaboom has U-turn), accounting for little amounts of chip damage you need, you basically win.
AND THEN you have Dire Claw. You managed to keep your Dondozo healthy if you have one, Sneasler user was stupid enough to set up already, now its time to wall it ou- oh wait it put your Pokemon to sleep while attacking. Or it got paralyzed and now you're being parahax. You'd be lucky if Dondozo was poisoned so you don't get paralyzed or put to sleep. Dire Claw is such a bullshit move. You have a 1/6th chance to put something to sleep, a 1/6th chance to paralyze them, and a 1/6th chance to poison them, while dealing damage. STAB 80 BP damage too. Steel types can bypass this because they are immune, but GUESS WHAT? Sneasler has STAB Close Combat. Basically ONLY Gholdengo and Gliscor care very little about Dire Claw thanks to their combined attributes, and Tera Poison/Ghost Garg too if you count it. Every other defensive check to Sneasler is always threatened by Dire Claw, and RNG that heavily favors Sneasler. When Dire Claw is used, you have a 1 in 5 chance to simply not be able to attack (P of para + full paralysis and sleep is about 20%), that also basically determines the game IF you manage to get Dondozo, Skeledirge, Clodsire, etc all healthy enough to beat Sneasler.
It's absolutely absurd that this thing wasn't banned since the beginning, wasn't banned as soon as Rillaboom got Grassy Glide again, and is being considered for a dropping back in OU. Is there like some new Psychic type version of Vacuum Wave that every Pokemon gets or something to warrant putting Sneasler with Pokemon like Gliscor or Urshifu-Water? Is there a leak that says Sneasler retroactively loses Dire Claw and Unburden in DLC2, replacing them with Splash and Truant, deleting all Sneaslers with those from everyone's boxes? Really, WHYYYY?