Elite 4 struggle

im basically getting slapped around by the elite 4 and im pretty sure my team has the backbone of a wet pasta noodle
my team is:
Sylveon, lvl 81, moonblast,bite,shadow ball, return.
giratina, lvl 85,aura sphere,shadow claw, shadow force, hex.
Mew, lvl83,flamethrower,fly,corrode, and surf(basically my only water move).
D scizor, lvl 98, low sweep,icicle crash,blizzard,night slash,item d scizorite.
D gallade(weakest member with bad stats and level), lvl 77, ice beam, icicle crash, thunder bolt, aerial ace,item d galladite.
D froslass,lvl 78,lava plume, crunch,shadow ball, eruption, item, d froslassite

i hope to beat the elite 4 with the pokemon i like without having to change too much, im gonna start grinding levels now, im not really good at comp pokemon so deciding moves isnt my strongest quality