This is stage-specific and related to one location in particular: Risky's Hideout, Stage 2.
This is a side-scroller left-to-right run with Mermaid Form running through. Best have the Mermaid Bubble for this run too. Either way, you'll end up wanting to destroy the mines, blocks, and fish, but keep the starfish alive. Get close to them and you'll charm them into your service, helping you by shooting their own bubbles with yours. There are only three to this run, and those are the three you need. You'll find them in the top first, then the bottom, and then in the middle of the pathways you'll go through, so be careful with your trigger finger.