Hi i got your request :D
Ok so the main problem i see with your team is no Rapid Spin user. That and the fact that this team will be switching around alot because it is Volt-Turn makes stall teams especially deadly in the way that they like to set up hazards while you won't be able to spin them away due to your team lacking Rapid Spin. Although you have two pokemon with Levitate your team will still be getting worn down quick. Sun teams also look quite deadly because of your two fire weaknesses and only one resist while your team also lacks a weather effect letting your opponents Chlorophy sweepers abuse double speed for the whole match.
The simplest way to fix this problem would be
Starmie>Mew I understand you lose one of the members from your "Volt-Turn chain" but Starmie provides alot for your team. For one he provides Water and Fire-type resistances which your team really needs seeing as it is weatherless so sun and rain teams don't rip you apart. Starmie also provides your team with the invaluable Rapid Spin support clearing hazards of your side so you can continue to Volt-Turn. You honestly don't really miss out on anything without Mew Jirachi already provides your team with a nice revenge killer while Starmie provides boltbeam coverage much like Mew. Starmie's last move is Hydro Pump which is his prefered stab move. With a Life Orb attatched Starmie can dish out alot of damage with his great coverage making him still keep up with the offensive nature of this team.
To help this team keep it's hazards on the field you might want to try
Suicide Lead Deoxys-D>Fast Spiker Set with Fire Gem and Hidden Power [Fire] Deoxys can set his hazards up and not let Ferrothorn set up his hazards or Forretress spin away hazards. This Deoxys-D set is designed to set up hazards then faint so you can bring in your other offensive pokemon in freely. He also has Psycho Boost to severly weaken Tentacruel, and Fighting-types.
Good luck with the team i hope i helped!
Sets
Tl;dr
~Superpowerdude