Hi, I'm back after thinking on Siglyph for a while.
Monkfish definitely has a point. +1/+1 Roob can punch it's way through your current Gliscor and your second fighting check, Siglyph, can't immediately threaten it at all. I'm going to suggest you try Bulky CM Rank over Siglyph. CM Rank still gives you the dual role of status absorber and defensive boosting sweeper, but Rank also serves as a more reliable, immediate answer to Roob and SD Birijion/Terakion, responding with STAB Psychic. With max Def investment it should also be able to take a +2 Leaf Blade and Stone Edge respectively. Rank contributes a lot of useful bulk that can cushion the blow from the aforementioned physical threats and being neutral to rock also helps. The standard set should get the job done.
Rankurusu @ Leftovers
Bold l Magic Guard
EVs: 252 HP / 252 Def / 4 SpDef
- Calm Mind
- Psychic
- Focus Blast
- Recover
Like several other posters, I think Dory would be a great fit on this team to replace Garchomp. I realize Garchomp is the centerpiece and certainly puts the team on its back at times by capitalizing on Sand Veil, but I think with his speed, Dory would make a more effective cleaner while also giving you some important revenge kills, particularly on +1 Urugamosu. Dory can also pick off a weakened Birijion or Landlos if they break through your intial check. The Dory + Rank/Gli combo shuts down a major threat to the current team, Balloon Terakion, forcing it to choose between SD or Rock Polish before getting popped. Right now, if it gets past Gliscor you just lose to it regardless, barring a Stone Miss miss. Rapid Spin support could be useful, but I think you'd benefit more from straight up SD with Return as the coverage option.
Doryuzzu @ Balloon
Adamant (preference) l Sand Rush
EVs: 4 HP / 252 Atk / 252 Spd
- Swords Dance
- Earthquake
- Rock Slide
- Return
Made him adamant because you don't really value the speed tie with opposing Jolly Dory considering you have Gliscor and Rotom. He could use the extra power for revenging Birijion and Rand.
The tweak on Rotom's spread should give some insurance against Landlos.
gl with the team son.