Gliscor:
Gliscor's set is good, but make its set Defensive, and Give it Stealth Rock to damage the opponent while switching in. Also, Gliscor overlaps types with two 'mons: Ground typing with Garchomp and Flying typing with Zapdos, so this team can be crippled by an Ice type. You can replace it with a Fighting type (Lopunny-Mega), or a Rock Type (Tyranitar / Mega), who counter Ice types (or Water types who has ice type moves) well.
- Mega Lopunny would first flinch the opponent with Fake out, and then finish with Close Combat, or switch out using U-Turn. It has incredible Speed and Atk, which is best suited for a Sweeper. Its Ability Scrappy helps it to hit even Ghost types.
- Tyranitar / Mega is a great support for Garchomp, summoning Sandstorm (My strategy is set up a Stealth Rock and switch out, and use these two 'mons at last). It can set up using Dragon Dance and raise its Poor Speed. Or it can directly use Rock Polish.
I would give sets of all.
Gliscor @ Toxic Orb
Ability: Poison Heal
EVs: 248 HP / 252 Spe / 8 Atk
Jolly Nature
- Protect
- Earthquake
- Stealth Rock
- Substitute
Lopunny-Mega @ Lopunnite
Ability: Scrappy
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Fake Out
- Close Combat
- Ice Punch
- U-turn
Tyranitar-Mega @ Tyranitarite
Ability: Sand Stream
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Earthquake
- Thunder Punch
- Stone Edge
Garchomp:
Three STAB Dragon type moves aren't required here. Dragon Claw is an okay move. Dual Chop is also an okay move. Scale Shot doesn't go well with Rocky Helmet, So you should have either Scale Shot or Rocky Helmet. You can use Outrage for power or Dragon Claw if you don't want to stick to one move for two to three turns. Now there are two spots left. One can be any Coverage move and other can be Swords Dance. If you didn't use Gliscor, give Stealth Rock to Garchomp. Go with this set:
Garchomp @ Rocky Helmet
Ability: Rough Skin
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Earthquake
- Outrage / Dragon Claw
- Iron Head / Stone Edge
- Stealth Rock / Swords Dance
Kartana:
Your set of Kartana is good.
Spectrier:
Using Rest without Chesto Berry or Sleep Talk is Kinda pointless. Rest definitely shouldn't be used on a frail 'mon. Spectrier's movepool is pretty shallow, but it is a great sweeper. I would suggest Will-O-Wisp + Hex, as it deals with Physical 'mons.
Spectrier @ Focus Sash
Ability: Grim Neigh
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Hex
- Dark Pulse
- Calm Mind / Nasty Plot
- Will-O-Wisp
Volcarona:
Three same type Fire Stab move here also? Remember that only one is required, especially in competitive. Charcoal also doesn't help much. Since it is frail physically, run Focus Sash. You also have an option to run heavy Duty Boots to avoid 50% damage from Stealth Rock. Also, Quiver Dance Volcarona is popular. Use Giga Drain for coverage.
Volcarona @ Focus Sash / Heavy Duty Boots
Ability: Flame Body
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Fire Blast
- Giga Drain
- Quiver Dance
- Bug Buzz
Zapdos:
Why both Thunder and Thunderbolt? If you want to use Thunder, why not Hurricane? You might want to use a neutral coverage move such as Extrasensory, or weakness coverage move (HP Steel / Ice). Use Electrium Z if you seriously need it, otherwise use Life Orb to deal more Damage.
Zappy Birb (Zapdos) @ Electrium Z / Life Orb
Ability: Static
Shiny: Yes
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Hurricane
- Thunder / Thunderbolt
- Defog
- Extrasensory / Heat Wave / Hidden Power [Steel] / Hidden Power [Ice]
Hope this helps :)
(My first RMT answer :))