Impressions:
Alrighty time to give some impressions of this funny scorpion guy, and honestly, I really like it!

Gligar @ Eviolite
Ability: Immunity
Tera Type: Ghost
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Earthquake
- U-turn / Knock Off
- Spikes
- Toxic
Gligar's traits are a blend of unique and useful, offering a spiker and pivot that can also defensive check Excadrill, Okidogi, Cobalion, and Thundurus-T, while also blocking Volt Switch from the latter two. Earthquake and Toxic together make it quite irritating to switch into, while U-turn allows it to pivot out on foes that are already poisoned. Additionally, U-turn lets it bring in teammates to more immediately threaten these foes like Latios or your own Thundurus-T, as well as pivot out on the two foes who can decently withstand everything that Gligar can do, Slowking and Tornadus-T. Although, Toxicing them leaves them much easier for teammates to beat down over the course of the game, especially in Torn's case as it lacks a recovery move. Knock Off is an alternative option for certain fatter teams that want Gligar to have a lasting impact in the match. Its ability to check Excadrill and Mandibuzz also allows it to keep a spike up in the face of removal due to it sponging all of their attacks in tandem with Immunity for Mandibuzz's Toxic, while threatening them with Earthquake and Toxic respectively. Tera Ghost allows Gligar to block Rapid Spin from Excadrill in the event that Gligar is in range to be taken out by Rapid Spin and Gligar's team really needs spikes to be up, however it should be noted that this very specific and it's rare Gligar wants to give up its amazing type.
Now, Gligar is not without its flaws, it notably lacks any way to heal so it tends to prefer to be on teams with more offensive teammates that can end the match quicker, however it can potentially be used on fatter styles if it can be assured its lasting impact will provide avenues to victory or if wish passers are used. Another flaw Gligar has is its low Special Defense, making it so that it can't withstand attacks from special attacking threats, however this isn't anything its teammates cant patch up.
Teammates:
Here are some mons that go well with Gligar from my experience.

Zarude @ Heavy-Duty Boots / Leftovers
Ability: Leaf Guard
Tera Type: Poison
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Power Whip
- Knock Off
- Swords Dance
- Jungle Healing
Probably the best teammate for Gligar imo. Remember how I mentioned Slowking is the one of the better foes to withstand Gligar's moves? What if you pair Gligar with something that bullies Slowking to hell. Zarude also provides a second Ground resist so that Gligar doesn't need to withstand as many attacks from opposing threats, while also removing foes' Heavy-Duty Boots with Knock Off so that Gligar's Spikes get more damage throughout the course of the game. In turn, Gligar can switch into the Okidogi and Cobalion that try to answer Zarude while also U-turning on Slowking so that Zarude does not risk a Thunder Wave or Scald burn that would force Zarude to waste a turn using Jungle Healing. However, the presence of Zarude may make the opposing Slowking too afraid to click anything other than Chilly Reception, so Gligar can abuse this fear to grab a Spike or Toxic.

Skeledirge @ Heavy-Duty Boots
Ability: Unaware
Tera Type: Poison / Fairy / Water
EVs: 248 HP / 16 Def / 180 SpD / 64 Spe
Bold Nature
IVs: 0 Atk
- Torch Song
- Hex
- Will-O-Wisp
- Slack Off
One issue some Gligar teams can have from my experience is susceptibility to set-up sweepers, so Skeledirge can help to remedy that. Skeledirge also loves having the opposing team worn down by Toxic and Spikes so that it may bust through the opposing team with Torch Song and Hex late game. Will-O-Wisp weakening opposing physical attacks can also help Gligar stay alive for longer throughout the course of a game, while Gligar also allows Skeledirge to not need to immediately use Tera in the face of an Excadrill. Gligar also allows Skeledirge to more easily use a Tera Type other than Poison given that Gligar can check Okidogi quite effectively, meaning Skeledirge can more easily use Tera Fairy to check Hoopa-U, Water to check Greninja, and so on.

Latios (M) @ Choice Scarf
Ability: Levitate
Tera Type: Dragon
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Draco Meteor
- Luster Purge
- Flip Turn
- Trick
Choice Scarf Latios was a pretty cool pairing on Gligar teams, as Latios checks tend to be pretty easy to wear down with Spikes up. Latios is also immune to opposing Spikes unlike the other two scarfers, Hoopa-U and Okidogi, meaning that it is less reliant on removal. It can also Trick its Choice Scarf to cripple an opposing wall both by locking it into a move and removing any potential boots, while Flip Turn allows it to pivot out and help rack up damage on switch-ins like Excadrill and Tyranitar.

Rotom-Wash @ Leftovers
Ability: Levitate
Tera Type: Steel
EVs: 252 HP / 168 SpD / 88 Spe
Calm Nature
IVs: 0 Atk
- Hydro Pump
- Volt Switch
- Pain Split
- Thunder Wave / Wil-O-Wisp
Provides a check to Tornadus-T that is immune to spikes and can both pivot and slow down foes so that they are easier to force out by teammates, can help the previously mentioned Zarude and Skeledirge find opportunities to break or clean respectively, meaning it also fits well alongside Gligar's teammates. It can also slot wisp if it wants to cripple physical attackers so that Gligar can better check them.

Slowking @ Heavy-Duty Boots
Ability: Regenerator
Tera Type: Fairy
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
IVs: 0 Atk / 0 Spe
- Scald
- Thunder Wave
- Chilly Reception
- Slack Off
Similar to Rotom-W just that it has Regen, can better check Excadrill, and packs a Fighting resist, while lacking a Spikes immunity, is slower, and can't run wisp (Scald doesn't count

).

Cobalion @ Leftovers / Rocky Helmet / Shuca Berry
Ability: Justified
Tera Type: Dragon
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Close Combat
- Volt Switch
- Thunder Wave / Taunt / Stone Edge
- Stealth Rock
Provides a secondary blanket physical check to help take some pressure off Gligar while also setting Stealth Rock, can also potentially use Taunt to help preserve hazards. Also appreciates Gligar's ability to check Thundurus-T so that it needs Stone Edge less, though Stone Edge is still an option for the hard hit on Zapdos.
General Teammates that Gligar May Appreciate, or Teammates that Appreciate Gligar:
Removal:

Gligar's lack of recovery makes it so that it would rather avoid chip from rocks if it can, so removal is appreciated even if it isnt strictly necessary.
Knock Absorbers:

Gligar really doesnt like losing its item so generally it likes having teammates that dont mind taking a knock that much.
Cleaners/Breakers:

etc.
Spikes are super neat for wearing things down into range for a breaker to punch through or for a cleaner to sweep.
Secondary Volt-Switch Blockers:

Zapdos poses a slight issue for some teams with Gligar as their only Electric immunity as Zapdos threatens heavy damage into Gligar with STAB Hurricane, so a second volt blocker can help remedy this. (Although, with Zapdos projected to rise to OU, this may no longer need to be considered come October.)
Other potential teammates that I considered but either couldn't figure out how to fit with Gligar or never got around to building a team with
Now for some teams with the Scorpion!
Gligar + Scarf Latios BO:

Gligar + Scarf Dogi BO:

Gligar Sand:

<-- not
amazing imo but its still kinda fun and can win games
Gligar + Umbreon Stuff:

<EXPERIMENTAL>
This last one was one I never properly tested, every other Umb + Glig team felt way too slow so this was the closest one to good I could find. In theory Gligar can check Cobalion and Okidogi for Umbreon while Umbreon passes wishes that help keep Gligar alive, but again in practice it felt like a rough fit. If anyone else wants to give either this team or one of their own a whirl, feel free. (This isnt entirely true anymore as I've gave it some games, feels alr but could maybe be a little better.)
I'll maybe add some replays later in an edit, was more focused on getting this post and some teams given that getting games that properly demonstrate a mon's traits on ladder is always hell for me lol.
Edit: Replays woo, will add more as i get them, also added a new "general teammates" section above so yay.
Edit 2: Outside of the second replay I've added another team.