@Riasiru  
In that case, it would be good to add the derpibooru exclusive tag.

@Riasiru  
Fixed.
 
Also, on another note, I made a mistake; Discord is Sans, Trixie is Papyrus, Starlight Glimmer is Asriel, and Starswirl is Gaster.

Source needed?… I’m the source… I literally made it… And uploaded it… THIS IS THE SOURCE!!! You are here!! RNA is short for Riasiru Neovas Artistry. What is my user name?

As a Slime, I disapprove of this.

@Align  
Nope.

@Joseph Raszagal  
Now I’m even more confused, thought maybe you were quoting something Discord would say…

@Align  
I was referring to Fluttershy being Papyrus.

@Joseph Raszagal  
Huh?

@Align
 
Everything must conflict. It is the true nature.

@Joseph Raszagal  
I wanna have Discord as Sans, for the rulebreaking and for showing you what happens to villains who go too far, but then Fluttershy would have to be Papyrus…

@Joseph Raszagal
 
Aaron looks a lot like Soarin’ to me.

@Daneasaur
 
Here’s my take on it:
 
Toriel -> Princess Celestia
 
Fisk -> Spike
 
Flowey -> King Sombra
 
Sans -> Rainbow Dash (the laziness, yet also great skill when not being a sleepy bum)
 
Papyrus -> Pinkie Pie (the general randomness, not to mention the desperation for friends)
 
Undyne -> Applejack (the sheer powuh)
 
Dr. Alphys -> Twilight
 
Asgore -> Filthy Rich? (I’m looking for a male character who means well, but can be mistaken for a villain)
 
Asriel -> Princess Luna
 
Mettaton -> Discord
 
Monster Kid -> Apple Bloom (because I made Applejack Undyne)
 
Napstablook -> Cranky Doodle Dandy
 
Temmie -> Snails
 
Bob -> Snips (if only because he appears to be slightly more intelligent than Snails)
 
Gerson -> Daring Do (just way older and senile)
 
Bratty & Catty -> Diamond Tiara & Silver Spoon (because duh)
 
Dr. W. D. Gaster -> Time Turner / Doctor Whooves (somepony has to be displaced between dimensions, right?)
 
And that’s it for now.

@Align  
Tirek as Flowey… Scorpan as Asriel?

Now I imagine Twilight as Frisk and the two holding hooves while crossing a spike puzzle c:

@Background Pony #FC4D  
I’d have Celestia as Asgore, Luna as Toriel - Luna doesn’t have the motherly air, but I can’t see Celestia abdicating because of a decision she doesn’t agree with.  
Flowey… Tirek maybe, what with stealing power and becoming huge. Would have to add a ton of headcanon to make Asriel work though.  
None of the characters really match up well…

Mettaton as Rarity, I suspect. (Or whatsername the model; Hoity Toity?)  
Scootaloo as that one monster kid, because RD is Undyne.  
NMM as Flowey? (Which leaves Luna as Asriel.
 
Though I’d say ‘Cadance as Toriel, [spoiler]Shining as Asgore[/spoiler’ myself. It keeps the ties without OC, allows Skyla to be Asriel; she’s a HasbrOC, so less issue there. And preempts the question of ‘Why are the ponies of the sun and moon UNDERGROUND?’
 
The window-washer pony from Rarity’s meeting with Fancypants as the burger-flipper guy.  
Granny smith et al as the bunny salesperson and family
 
The generic red-and-black alicorn OC as So Sorry or Glyde.
 
Diamond Tiara and Silver Spoon as Catty and Bratty.(Or vice versa.)
 
I’d say make Maud into Sans and Pinkie into Papyrus. Pinkie’s the more active, silly, excitable one. Maud is quieter, and more likely to give something a bad time.

Celestia as Toriel?
 
aaaaaaaaaaaaaaaa

So I guess this makes Spike the protag, undyne is RD, Dr. Alphys is twilight, Pinkie is Sans.
 
i’ll need to finish it before I can think of a full roster for the 7.

Sorry, but you’re no substitute for Goatmom herself.