Nope, it's not one of the characters.
Nor is it the Dusk Nobody, the Doppelganger, or Hollow Bastion in KH1.
The word 'crescendo' usually means a gradual increase of volume in music, but not in this case.
It can also mean an increase in speed or intensity.
And my score on that IQ test came out as 142...don't know how accurate that test is though.