Reaching World 5 in New Super Mario Bros. (DS) — Simple Progression

World 5 unlocks automatically after beating World 4's castle. There's no shortcut or hidden requirement.

Progression Path

1. Clear World 1 → World 2 unlocks.
2. Clear World 2 → World 3 unlocks.
3. Clear World 3 → World 4 unlocks.
4. Clear World 4 (including castle boss) → World 5 unlocks.

Each world has 8–10 levels + tower + castle. If you're stuck, use Star Coins to unlock mushroom houses for power-ups, or watch a walkthrough for the specific boss.