For singles, what MudkipLegend suggested is very viable. Also just realized none of your pokemon can run trick room (I think). If you are running specs Sylveon, remove draining kiss and helping hand for moves with better coverage. My specs Sylveon runs the following moves : Hyper Voice, Psyshock, HP Ground, and Shadow ball. HP Ground is so nice because it let's Sylveon hit 5 different types, most importantly steel types, for super effective damage. If you are running leftovers Sylveon, I see a lot of things you can do. Toxic, Wish passer, Calm mind. It's up to you. Other than that, I think this is a very solid team for singles. I would definitely have a hard time with this one.
For doubles, I think one of the most important things a developing competitive battler should know is how important protect is. Whether it is to scout, or stall out a turn of burn, tailwind etc, you always want to run protect on a non-supportive pokemon if you can. On Blastoise, I would get rid of Dark Pulse for Protect. It gets boosted by mega launcher, but ice beam is so much more important when you look at pokemon used in VGC this year. For Rhyperior, I would replace Megahorn for Protect. Megahorn is very powerful but you will see how much more important protect is. Plus, if you have Gliscor in at the same time and another pokemon threatens Rhyperior, you can protect and then earthquake. Just an example of many situations. If you really don't want to replace it though (which I think you should though), I would run assault vest Rhyperior. He will be a tanky set that can deal massive damage. I would reset the EVs with a reset bag and give HP and Attack for the second one though. For Rotom Heat, I would take off the scarf. You never want to scarf yourself into Will-O-Wisp. At the same time, you don't want to replace Will-O-Wisp because you definitely want to cripple pokemon like mega-khangaskan. I would put safety goggles or sitrus on Rotom Heat. Safety goggles will counter spore from pokemon like amoongus or t-waves from prankster thundurus. I would personally also replace dark pulse with thunderbolt because volt switch is not a guaranteed OHKO on pokemon like talonflame, and thunderbolt is if it is standard build. for Aegislash, I would replace Shadow sneak for wide guard. Wide guard is such a clutch move that allows you to protect your team from incoming earthquakes, Rock Slide etc and retaliate with your other pokemon. It will come much more in handy than shadow sneak in my opinion. Gliscor looks fine to me. I would personally replace roost with protect,toxic, or tailwind. Since your team can't learn trick room, having that tailwind support can put so much momentum in your favor. That is just me though. For Sylveon, I would have leftovers. Specs is nice, but you never want to lock yourself into any non-damage move. I would also replace draining kiss for shadow ball, HP Ground, or Protect. I personally would go protect for that extra leftovers recovery. With these adjustments, I think your team will be a real threat in doubles.
Edit: I was too lazy to think of a switch out pokemon so I worked with what you had :D
For doubles, I think one of the most important things a developing competitive battler should know is how important protect is. Whether it is to scout, or stall out a turn of burn, tailwind etc, you always want to run protect on a non-supportive pokemon if you can. On Blastoise, I would get rid of Dark Pulse for Protect. It gets boosted by mega launcher, but ice beam is so much more important when you look at pokemon used in VGC this year. For Rhyperior, I would replace Megahorn for Protect. Megahorn is very powerful but you will see how much more important protect is. Plus, if you have Gliscor in at the same time and another pokemon threatens Rhyperior, you can protect and then earthquake. Just an example of many situations. If you really don't want to replace it though (which I think you should though), I would run assault vest Rhyperior. He will be a tanky set that can deal massive damage. I would reset the EVs with a reset bag and give HP and Attack for the second one though. For Rotom Heat, I would take off the scarf. You never want to scarf yourself into Will-O-Wisp. At the same time, you don't want to replace Will-O-Wisp because you definitely want to cripple pokemon like mega-khangaskan. I would put safety goggles or sitrus on Rotom Heat. Safety goggles will counter spore from pokemon like amoongus or t-waves from prankster thundurus. I would personally also replace dark pulse with thunderbolt because volt switch is not a guaranteed OHKO on pokemon like talonflame, and thunderbolt is if it is standard build. for Aegislash, I would replace Shadow sneak for wide guard. Wide guard is such a clutch move that allows you to protect your team from incoming earthquakes, Rock Slide etc and retaliate with your other pokemon. It will come much more in handy than shadow sneak in my opinion. Gliscor looks fine to me. I would personally replace roost with protect,toxic, or tailwind. Since your team can't learn trick room, having that tailwind support can put so much momentum in your favor. That is just me though. For Sylveon, I would have leftovers. Specs is nice, but you never want to lock yourself into any non-damage move. I would also replace draining kiss for shadow ball, HP Ground, or Protect. I personally would go protect for that extra leftovers recovery. With these adjustments, I think your team will be a real threat in doubles.
Edit: I was too lazy to think of a switch out pokemon so I worked with what you had :D
