Now, even though there is a good answer, i'll be answering.
Ditto is a great Pokemon but i don't know about the Nature and EV Spread you gave it. Bold will be decreasing his Attack and it's unfortunate if you switch in on a Physical Pokemon. I recommend Sassy Nature (+SDef,-Spd) and this EV Spread: 252 HP / 4 Def / 252 SDef. Of course, your EV Spread is just fine. Remember that Ditto's role is to switch in on set-up sweepers. BTW, don't use him as a lead and remember he'll be soon shifting tiers (all the way to OU). Have fun with him while you can.
On to Miltank now. He's part of your defensive core, right? We'll be giving him a Defensive shift, so he'll be a Special Wall now. Switch EV Spread to 252 HP / 252 SDef / 4 Atk and give him Careful Nature. Keep Thick Fat and you'll see why with the next Pokemon....
Shelgon! With Eviolite, he makes an excellent Defensive Pokemon. He performs a good Defensive core with Miltank, who can take Ice attacks with ease because of Thick Fat. We'll be replacing Misdreavus for him, unfortunately destroying your core. Eh, you'll find him better than Misdreavus :]. I have two sets for him, choose the one you like the most.
Shelgon @ Eviolite
EVs: 252 HP / 236 Def / 20 Atk
Impish Nature (+Def, -SAtk)
- Dragon Dance
- Sleep Talk
So Smogon calls dis set ''Bulky Dragon Dance''. It doesn't have this name for nothing, as it is virtually impossible to kill without a STAB Special Attack. Dragon Dance boosts his already high Attack and awful Speed to awesome and usable, respectively.
''Outrage is superior to Dragon Claw because Outrage will not have the
locking and confusion effects if selected by Sleep Talk.'' -Smogon
Exactly why Outrage is here. So ResTalk combination brings him back to full health, making him awfully hard to kill and may have the side effect that your opponents might want to kill you. At least they don't have your address ;D
Ninjask is in no way supporting your team and you don't even have Baton Pass on him, which is the only reason why you'd even use him. Instead, i suggest Rotom-S.
Rotom-S @ Choice Scarf
EVs: 252 SAtk / 252 Spd / 4 Def
Timid Nature (+Spd, -Atk)
- Volt Switch
- Hidden Power [Grass] / Thunderbolt
- Air Slash
Of course, one of my favorite NU Pokes. Volt Switch is STAB and is a must-have on him. Trick screws over walls while Air Slash is STAB. 3rd moveslot is your choice. HP Grass is coverage against those nasty Rock types while T-Bolt is STAB and is if you plan to stay in.
Alomomola is perfect, don't forget to give credit to Mike for the awesome set.
To round out your team, we'll be replacing Vileplume for a Special Attacker. I suggest my favorite tank, Musharna. I would suggest Riles Gardevoir like i was planning to do but i would look like a copycat so.... yeah.
Musharna @ Leftovers
EVs: 252 Def/ 228 HP/ 16 SDef/ 16 SAtk
Bold Nature (+Def,-Atk)
- Calm Mind
- Signal Beam
Smogon's set with a slightly altered EV Spread. 16 SAtk provides a tiny bit more ''sweepiness'' with Calm Mind. Calm Mind makes him a Specially and Physically defensive beast while having great Special Attack. Moonlight shrugs off all damage taken while set-upping or sweeping. Psychic is STAB while Signal Beam is coverage against Dark types.
Ok, so i hope i helped you. Beware of one thing though: Once Rotom-S and Ditto are dead, Shedinja sweeps your team. Hopefully, that won't happen.