A continuation of an idea presented here . If Cozy's Junko, then let's speculate which MLP characters could substitute other DR chars. I`ll go through DR2 characters (since that bunch is the best out of all three games in my opinion and they're also Ultimate Despairs).
I'm picking only schoolchildren, both from Twilight's school and Ponyville elementary.

Hajime Hinata — Pipsqueak
Talentless (yet) and a dork. (shrugs)

Chiaki Nanami — Button Mash
Duh.

Sonia Nevermind — Silverstream
A naive foreigner with a positive attitude. Plus, she's totally shippable with Gallus.

Akane Owari — Yona
Eats a lot, punches stuff a lot. Loud and energetic.

Hiyoko Saionji — Babs Seed
One of the least fitting choices on the list, but, eh, can't win it all I suppose. However, she's got a capacity to be a bully and self-esteem issues.

Gundham Tanaka — Gallus
Brooding boy with a heart of gold. All he needs now is a hamster army.

Kazuichi Soda — Snails
Second thirsty after Snips. Looks like a punk too.

Mahiru Koizumi — Smolder
«You're a dragon, right? Then act like it!»

Teruteru Hanamura — Snips
Complexion fits, and I can easily imagine Snails to be a little bit too thirsty.

Nagito Komaeda — Sandbar
Messy hair, dorky, probably gay. «I want your friendships to shine!»

Nekomaru Nidai — Applebloom
Strong, courageous, and she even trains other people too as a cutie mark crusader.

Ibuki Mioda — Sweetie Belle
Basically, music connection.

Peko Pekoyama — Scoots
Possess a fighting spirit and fits well with Rumble being Fuyuhiko. At least in my head.

Mikan Tsumiki — Twist
A soft-spoken punching bag.

Fuyuhiko Kuzuryu — Rumble
Grumpy, uncooperative, wants to stand on his own without his family.

The Ultimate Impostor as Byakuya Togami — Ocellus as Diamond Tiara
Obvious choices, both for the impostor and for Byakuya. During the time in school Ocellus impersonated Featherweight (Ryota).