Sly tends to be normally quiet, and not talk too much unless he's interested (such as his interest in Yusei's "Stardust Dragon" card). He also can be blunt (as seen when he didn't care for Jack being arrested, and stated "I always knew Jack would do something like this one day. That's what he get's for being too arrogant"). In the dub he has more of an attitude and even insults his classmates by calling them "brain dead lame wads", and is far more wanting Yusei's "Stardust Dragon", claiming he'll do anything to get it.
Sly shows a high interest in Yusei Fudo's "Stardust Dragon" while helping to pick up Yusei's cards. Although Luna appears to interact with him more than the others do, he doesn't seem to care very much and just ignores her. Like the other students, he was going to be expelled from the Duel Academy by the teacher Rudolph Heitmann, until Yusei challenged the instructor to prevent this. After Yusei defeats Rudolph Heitmann in a Duel, ensuring that the students don't get expelled, Sly thinks Yusei's a lucky and that he wants his "Stardust Dragon". However, he is never shown to act upon this statement.