Is Arlong Still in Impel Down?

Arlong is released from Impel Down when Jinbe became a Shichibukai. Arlong had a fight with Jinbe and started the Arlong Pirates and went to East Blue and settled on Cocoyasi Island.

Is Arlong still alive?

Based on the wiki, Arlong is still alive. Also, based on Reddit, looks like this is from chapter 634, but from unofficial/incorrect translation.

Who is in Level 6 of Impel Down?

Devon, also known by the epithet of Crescent Moon Hunter, was locked up in Impel Down Level 6, just like Avalo Pizarro. She's known to be the most dangerous female pirate in the history of One Piece, which solidifies her reputation as one of the strongest in the series.