Zelda Breath of the Wild – Can You Get the Master Sword with Yellow Hearts?

The following items can only be obtained in one way:

• Master Sword
• Hylian Shield
• All the Champion weapons
• Cerimonial Spear
• Rubber Armour Set
• Barbarian Armour Set
• Climbing Armour Set
• Zora Armour Set
• Old Shirt
• Old Trousers
• Snow Boots
• Sand Boots
• Thunder Helm

• "Of the Wild Armour Set"

All items that can only be obtained in one place (except the Nintendo Switch Shirt) and don't respawn can be re-obtained either by remaking them (in the case of the Champion weapons), or can be purchased from a special store.

Spoilers for the store:

You must complete the quest "From the Ground Up", which is unlocked after purchasing the house in Hateno Village. After you've fully built the town, and NPC will spawn on the roof of the building right of the entrance of Tarry Town. Speak to him. He can sell anything that can only be normally obtained once in the game, bar the Master Sword, Cerimonial Spear, and Champion Weapons

Enemies are not scaled to your game progress. Rather, enemies are scaled to how many enemies you have killed. The more Bokoblins, Moblins, Lynels, etc. that you kill, the more likely you are to encounter blue, black, and silver variants.