** SPOILERS **
This post will reveal the entire worked solution to this riddle.  If you're still working on it, stop reading here!

The Riddler is no help at all here; he just points out the obvious, that we're facing what looks like a Dance Dance Revolution layout.  We see five songs, each of which contains ten movement groups – five of Harley's and five of ours, except for Song 5, which contains six of Harley's and four of ours.

Lacking guidance from the Riddler, we look at each song and see if we can pick out some kind of pattern.  We might suspect that we're looking at a code made out of DDR arrows.  Looking at Song 2, we notice that the song uses only left and right arrows, which reminds us of the dots and dashes of Morse code.  If Song 2 is really Morse code, it turns out that the left arrow can't be the dash, because there is no Morse code letter that goes dash-dash-dash-dash like the third movement group.  So the left arrow is the dot and the right arrow is the dash.  Harley's part of Song 2 then deciphers to FGHIJ, while ours is FNOBO.

FGHIJ looks suspicious.  Noticing that Harley has 26 movement groups, the same as the number of letters in the alphabet, we now suspect that Harley is merely reciting the alphabet: her Song 1 is probably ABCDE, her Song 3 is KLMNO, and so on to Z.  We should think about other ways to code a letter using arrows, using the reasonable guess that Harley's dance is going through the alphabet for guidance.

In fact, each song uses a different code.

Song 1: Binary.  Each arrow is a binary place value, so Harley's dance goes 0001, 0010, 0011, 0100, 0101.  These are the binary values 1, 2, 3, 4, and 5, corresponding to the letters ABCDE.  Our dance goes 1110, 0001, 1101, 0101, 1111.  These are the binary values 14, 1, 13, 5, and 15, corresponding to the letters NAMEO.

Song 2: Morse code.  Left arrows are dots, right arrows are dashes.  Harley's dance goes ..-. / --. / .... / .. / .--- , which translates as FGHIJ.  Our dance goes ..-. / -. / --- / -... / --- , which translates as FNOBO.

Song 3: Pointing at the answer.  If you start in a Song 3 movement group and then move around the chart according to the arrows, you land in the movement group with the correct letter.  All of Harley's dance moves cancel themselves out and land back in their own boxes, but by now we are pretty sure they must be KLMNO.  Our first move takes us left two and up two, to a cell in Harley's dance that we know is D.  Our second move takes us up two and right two, to a cell that we can guess is Y – and so on.  In sum, our dance in Song 3 translates as DYOWE.

Song 4: Drawing the letter.  If you put your pencil on a piece of paper and move it up, down, left, right, or diagonally according to the arrows, you sketch the encoded letter.  Harley's first move takes the pencil up twice, then right, then down, then left, making a capital P.  Her second move goes left, up, right, down, and then down and right diagonally, making a Q.  In sum, her moves translate as PQRST, and ours translate as NSCRE.

Song 5: Semaphore.  Semaphore uses two flags to indicate a letter.  Each movement group has two steps, each representing a flag.  Harley's first group is up-left and up-right, which is semaphore for U.  In sum, her moves translate as UVWXYZ, while ours translate as ATOR.

In total, Harley has spelled out the alphabet, while we have spelled:
NAMEO / FNOBO / DYOWE / NSCRE / ATOR
or
NAME OF NOBODY OWENS' CREATOR

Nobody Owens is the protagonist of The Graveyard Book, written by Neil Gaiman.  The answer to this riddle is thus NEIL GAIMAN.