Poe

In Ocarina of Time and Majora's Mask They can easily be defeated by slashing it with the sword. After that, you can catch their spirit in a bottle. Drinking it will usually make you recover health, but it can actually damage you as well. They can be found in Kakariko Graveyard in Oot and Stone Tower Temple in MM. Note that they'll become invisible for a while when targetting them, so you'll have to refrain from doing that.

In tWW, you must first shine light on them with the Mirror Shield, and only then can they be harmed. They will then run around the room frantically. Occasionally, they'll possess you, causing the controls to reverse. They appear in the Earth Temple.