If you loved One Piece: Dead End Adventure, try One Piece Special: Open Upon the Great Sea! A Father's Huge, HUGE Dream!
A bridge between a film you've already seen and one most people haven't. One Piece Special: Open Upon the Great Sea! A Father's Huge, HUGE Dream! has roughly 9.8× fewer votes than One Piece: Dead End Adventure — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.

One Piece: Dead End Adventure

One Piece Special: Open Upon the Great Sea! A Father's Huge, HUGE Dream!
What they share
Both films are directed by Konosuke Uda, and they both carry the playful mood tag, and they sit in Action / Adventure / Animation territory. If that's the register that drew you to One Piece: Dead End Adventure, the second film will land in a comparable space — through a different lens.
What One Piece Special: Open Upon the Great Sea! A Father's Huge, HUGE Dream! is
You’re pirates with empty pockets and the kids know where the gold is buried. Then Luffy and crew pull anchor right into the mess. The treasure map only works when Amanda speaks her father’s forgotten phrase. The director frames every chase as a cartoon rave—colors bleed like ink in water.