Helix could try to break into Eridan's hive, which is a pirate ship he built in the largest building he could find in Marina. Only issue is his guard shiny Horsea, who would pretty much attack on sight (by which I mean, if he wants to get blasted with water and ink by a tiny angry Pokemon, feel free to do that).
You'll also earn Eridan's ire if anything, AND I MEAN ANYTHING, is stolen.
Especially if it's one of his hidden buckets, I mean what there aren't any of those in his hive...