First off why have d charizard, giratina, and garchomp instead of more spread out coverage? Second, you’re going to want to update your movesets for your pokemon badly. Thirdly, you’re not optimizing items on your mons either.
My suggestions: replace sceptile with thick fat ability delta snorlax (adamant/careful nature) with leftovers that knows drain punch, seed bomb, earthquake, synthesis/belly drum. Give d. charizard (hopefully modest/timid nature) the mega stone to set up new moon weather and use shadow ball, dragon pulse/draco meteor, flamethrower, sludge bomb/shadow sneak. Hustle ability D. Scyther (jolly nature) should be given focus sash and know hone claws, close combat/drain punch, icicle crash, and shadow claw.
I’ve got plenty of other suggestions, but that’s what i’ll offer for now
I recommended substituting garchomp and giratina because you’ve already got dragon type covered w/ delta charizard. Plus earthquake is a common coverage move, so garchomp’s ground typing isn’t necessary either. I’d personally replace them with jolly delta haxorus (you can run either water veil or strong jaw set) and delta chandelure. Delta chandelure will definitely help with shadow mewtwo given it’s fairy typing and flash fire ability. I ran my delta haxorus with an expert belt, while delta chandelure could work well with either choice scarf or choice specs. You’d need to teach delta lampent moonblast before evolving it though, since delta chandelure can’t learn moonblast by using heart scales.
You have a couple of choices for D. Haxorus, as it’s got two useful abilities depending on which you prefer. People tend to lean towards water veil ability and a swords dance, aqua jet, iron head, earthquake combo. I’ve also run mine w/ strong jaw where it knows aqua tail, iron head, crunch, and ice fang. mostly focusing on making use of coverage for that set, but is prone to burns unlike the water veil set.
For delta litwick I believe I just used an oran berry
what level does it learn ice fang/aqua tail/iron head? it’s move set right now is heavy slam, swords dance, brine, metal burst. strong jaw and modest nature
I’m not sure off the top of my head, so i’d check the wiki which will list all the moves any pokemon can learn and how they learn them. I’d also do whatever is necessary to change that nature. there’s pokepon, but probably easier to just trade someone for a jolly natured one.