Enemy prize packs
From ALttP Speedrunning Wiki
Every enemy sprite is part of a group. Each group have their own "prize pack", meaning an ordered list of what they will drop when you kill them.
The first time an enemy in a specific group drops an item, you will always get the first item in that pack. And next time the second etc.
Each group have their own "counter", so advancing one prize pack does not affect the others.
Most enemies have 50% chance of dropping, some have 100%.