"A bonus which increases Link's experience points. Watch out! Enemies sometimes pop out of them too!"
Zelda II: The Adventure of Link manual
P Bag

P Bags are items from Zelda II: The Adventure of Link. P bags give Link between 50 and 500 Experience, and are very helpful for leveling up. Some are found in set areas and do not respawn once Link collects them. Every tenth strong or weak enemy Link defeats will drop either a P Bag or a Magic Vial. With the exception of blue Moas, which drop 50 Experience P Bags, all enemies worth 20 Experience or less drop 50 Experience P Bags, and all enemies worth 30 Experience or more drop 200 EXP P Bags.

The text in the manual is incorrect in that enemies do not pop out of them.

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