Ok, lets try this out:
Mega Wigglytuff
Type: Normal/Fairy
Ability: Prankster
Hp: 140
Attack: 70
Defense: 70 (+25)
Sp. Atk: 135 (+50)
Sp. Def: 70 (+20)
Speed: 50 (+5)
Stat Total: 535 (+100)
New Moves: Boomburst, Calm Mind
Description: What do you know the Jigglypuff line most for? Perhaps the fact that Jigglypuff loves it's singing. So, to bring it back to that, Mega Wigglytuff is going to have a fresh Prankster ability to make sure it can get it's sings off before the opponent can land a hit hard enough to defeat it. So, since Mega-Evolving into prankster will activate the ability next turn, Wigglytuff could run a set of protect, sing, boomburst, and calm mind, allowing this pokemon to Mega-Evolve, protect, get the prankster sing off, calm mind up, then boomburst sweep.
Mega Delcatty
Type: Normal/Dark
Ability: Darkness Dash(Gale Wings clone for Dark Type Moves)
Hp: 70
Attack: 135 (+70)
Def: 45 (-30)
Sp. Atk: 75 (+20)
Sp. Def: 35 (-30)
Speed: 140 (+70)
Stat Total: 480 (+100)
New Moves: Knock Off, Extreme Speed
Description: Delcatty is normally an all-around pokemon with not that good stats. So, making a mega for it would definitely be interesting For this submission, I went with a strong, physical attacker, with some good Sp. Atk too, and that had a lot of speed. This, overall will make it an all or nothing attacker, in which one attack could easily cripple this pokemon. So, I gave it two typings, Dark and Normal, which seemed to fit it well, and a gale wings clone that will allow Delcatty to easily knock off any items that could possibly hurt Delcatty in any way. Along with this, I gave it extreme speed, in case if it isn't fast enough. A good moveset for this may be Knock off, extreme speed, fake out, and play rough, giving it great coverage for any types that could counter it.
Mega Musharna
Type: Psychic/Fairy
Ability: Adaptability
Hp: 116
Attack: 55
Defense: 120 (+35)
Sp. Atk: 127 (+20)
Sp. Def: 140 (+45)
Speed: 29
Stat Total: 587 (+100)
New Moves: Hyper Voice, Sweet Kiss
Description: Musharna already has a good bunch of moves, and with adaptability, moves like dream eater and dazzling gleam do even more damage. Really, Musharna can run many sets revolving around certain moves such as Hypnosis, Calm Mind, Rest, or Sweet Kiss. This Pokemon probably had the most possibilities on what it could be overall.
Edit: Made it so that Delcatty's defenses are even lower and speed/attack is even higher to be able to move along with the fastest.