I don’t like your Giratina, having 3 ghost-type attack doesn’t seems productive enough. Whitout rain support, I don’t recommend Livewire. I also suggest you run only one Mega Evolution per team to maximise your use of item per battle.
Have you defeated the E4 yet or you want some tips?
I would go with a dragon move (do you have the TM for dragon pulse?). I always want to have an attack move for each type, just to double up on STAB+super effective possibilities.
I would use a cmind giratina. Use rest(optional, you could also use hyper potions and replace this with another move), shadow ball/dragon pulse, will o wisp/toxic(will o wisp if they have lots of physical attackers), and cmind. Giratina’s spatk isn’t great, but its really tanky, so you can usually set up cmind really easily. Most of the time you can get to 4x spatk and 4x spdef, and then sweep. Put a leftovers on it if you use this method. If you continue to use an offensive gira, take out 2 of the ghost moves.
Personally, I would not reccomend setting up stealth rock and spikes. It takes too long and the other pokemon can usually 2hko or ohko your mew.
Use a fast taunt pokemon to counter the baton pass person so that their smeargle can’t do anything.
Vary your pokemon throughout the e4. You can’t change pokemon, but you can switch movesets and items to counter each person.
Flygon is meant to be a phsyical attacker, get rid of dragon voice, bug buzz, and boomburst. I would use ddance, outrage/dclaw, and roost
Bug Buzz hits dark, grass, and psychic. You otherwise have coverage for all three of those. If you really want a bug move on it, U-turn does higher damage than bug buzz even if it has a modest nature.