Rook c1
 
According to Stockfish Sunset missed closing out the game with Queen b1. Qb1 is advantageous (-4.65), but in a novice game this gives a chance for Sunset to blunder and Twi to come back. After all she has more material and black’s king is out in the open.
 
If Sunset played Rook c1 instead she would have checkmated Twilight after 9 moves:  
1. … Rc1 2.Bd1 Qc4 Bishop body blocks the rook, black queen moves to block e2 & f1  
3.Nf6+ Kf7 4.Ra1 Rxa1 Twi checks the enemy king and forfeits her rook. Even Applejack would give up here.  
5.f4 Rxd1+ If the King recaptures then the other rook comes to the first rank. That would be checkmate.  
6.Kf2 Qxf4+ 7.Kg2 Rb3 8.Nfe4 Qf3+ 9.Kh2 Rxd2+ 10.Kg1 Qg2# 0-1

It’s not quite checkmate. Twilight can defend by moving her bishop between her king and Sunset’s queen. However, I think Sunset could still pull off a victory this way. If she responds to that by moving her rook back to be directly next to the bishop, then she can counter the defense pretty easily. The bishop is stuck there, the king can only move directly away from it and Sunset’s pieces, Twilight’s rook can’t do anything without putting itself in the line of fire without actually changing the situation, and any defensive play or check she could set up with her knights would take too long to do any good. From that point, it would be fairly straightforward for Sunset to maneuver her other rook and queen into position to set up an actual checkmate. Of course, the fact that Twilight still has both knights does complicate that.

well sunset play with celestia so is normal can beat twilight(human) on this game!

@Background Pony #C607  
I think her shirt is just one of those with openings around the shoulders for some reason.

So, are sunset’s “sleeves” actually sleeves or bands around her upper arms? They definitely appear to be the latter here.

Thanks for not flipping the board at her face, Twilight

@Background Pony #DBCB  
Yeah, I’m chalking that up as an animation error. No way would both Sunset and Sci-Twi miss that. :)

The position of chessboard is wrong.
 
Right bottom corner to every player should be white, not black.
 
Either the girls are too caught up in a game to notice that they should turn the board 90 degrees, or animators are just being lazy.

@Josh103  
https://www.youtube.com/watch?v=dFlOZFSIsMQ

@Derpinator  
And, thanks to her background as Celestia’s student, probably has a broader education than Sci-Twi.

Sunset vs Sci Twi: the rematch (complete fight)

Sunset is not very studious as Sci Twi.But it dominates chess (sport science)

@Josh103  
It’s pretty close to one though. Like a few moves close.

It’s not a checkmate though.

@Background Pony #C6D6
 
Nope, you’re right. I miss-remembered something else.

@MrSeyker  
Unless it’s a joke (which doesn’t seem to be) I mean I literally searched on Derpibooru and nothing seem to be showing Sunset Shimmer playing chess with Sci-Twi “in the books” except this one

@MrSeyker  
I guess I missed something. In which Short/Special/movie did this happen anyway?

Silly Sci-Twi. You forget that Sunset is just as much an intellectual as you.

@Background Pony #6CA2
 
They have played before in the books. Sunset won there too.

@Background Pony #1D22  
I don’t think she was good at chess until Sci-Twi train her I guess

@Josh103  
It’s funny because that appears to be a bishop in front of Twi’s king and not a pawn, so it’s not checkmate.

Even in chess she is perfect.

Or is that the Colombian word does not tell you anything

That’s how obvious I am ?

@colombiabrony  
>what you just said  
>is it an actual sentence  
I can tell that english isn’t your first language. Try and type that again.