1.

The Trading Sequence is required — Magnifying Glass reveals hidden dungeon entrances.

2.

Marin can sing Ballad of the Wind Fish when you bring her to Manbo's Pond.

3.

Secret seashells unlock the Level 2 Sword at 40 shells — hugely powerful.

4.

The Color Dungeon (Switch remake) rewards you with Red or Blue Tunic.

5.

Bow-Wow from Madam MeowMeow can eat enemies — borrow him for the 2nd dungeon.

6.

The ending changes based on how many times you've died — aim for zero deaths.