1) Gligar
2) Swirlix
Gligar has 19 Speed, a great typing, amazing physical bulk combined with decent special bulk, two really strong offensive moves, and a support movepool other Pokemon could only dream of including Stealth Rock, Defog, U-turn, and Knock Off. All of these attributes combined make Gligar a tier above all of the rest of the LC Pokemon. There is very little reason not to use Gligar on a team because it just does so much while being difficult to punish. There are few reliable answers to Gligar, as many are invalidated once their item is Knocked Off or weakened just a little bit, or lose to Gligar carrying a specific move like Knock Off or Agility. While normally usage is not the most compelling argument for banning, Gligar's 77% usage in SPL is a testament to how easily it fits on a team. One could argue Gligar makes a lot of Pokemon more manageable, and while that is true, banning it is worth the tradeoff otherwise Gligar will continue dominating the tier.
Swirlix has three potent setup sets that require wildly different counters for each. Belly Drum OHKOs most of the tier after a boost, Cotton Guard + Calm Mind is impenetrable without phazers or really strong Special Attackers, and CM sets up effortlessly while doing good damage. The worst part about all of these sets is Swirlix sets them up very consistently thanks to the recovery provided by Berry Juice, so unless you play really well, good luck trying to prevent a Swirlix from setting up. Swirlix is also almost impossible to revenge kill because it outspeeds even the boosted tier, aside from Chlorophyll Bulbasaur and 19 Speed Choice Scarf Pokemon.