I think Celebi's role is overextended, as a lead rock setter and a crippler at the same time. Change Chomp to act as a lead (defensive or offensive) and change Celebi from SR to Earth Power to have one more Ground attack for Heatran. Also give Weavile Low Kick/Brick Break over something, preferrably Pursuit. You have only one Mon that takes normal damage from Psychic type Stabs, whatcha gonna trap, Gengar? Also Starmie, Weavile and Celebi are weak to UTurn, so there are some scarfers out there that will chip them dead.
If the game plan is to destroy every Steel in existence to open way for Mega Gardevoir, ok. But your team is glassy, Weavile and Starmie will bleed on their Life Orbs, you have 0 speed boosting moves and Gardevoir has a meh speed herself. I'd axe Celebi and that big U-turn weakness to add Talonflame with a Ground Type Natural Gift to deal with all the Fighting threats Jelly listed without having Celebi trying to check them, set rocks and cripple at the same time. Just Birdspam them, Roost and continue. I would also put Shadow Ball on Garde, kill the steals with the rest of the team and use SB to hit Mega Meta on the switch, since it's the toughest one to handle for your team. This strong priority also allows you to not go Scarf on something.
Also I'd like more of a PumpBoltHPFire Starmie to kill any Steel trying to hide there. And Magnezone needs the Scarf to move before that +2 Superpower from Scizor, Tough Claws Hammer Arm and EQ from Mega Meta.
I also think you like that faster style more than tanking and crippling.