To progress any further, you need to head to The Veil and find someone there. He won't talk to you immediately, so you've got to chase him for a little bit. Once you've cornered him and interacted, examine the crates where you'll be to find a familiar symbol. You should know what to do from there.
The game-breaking thing involves using Fish or Nature form to bypass the giant tentacle thing in The Abyss. You're not supposed to do that yet, so don't go down through there or you'll miss a whole level and a lot of plot.
