Boo

are enemies in. They are directly based on the enemies from the  series.

Characteristics
Boo Buddies only appear in a single dark room in the Bottle Grotto, housing the Power Bracelet. Unlike their Mario counterparts, which are typically shy and hide when stared at, they do not shy away from Link and actively pursue him in the darkness of the room. When struck with the Sword they disappear, only to reappear elsewhere and continue their assault. They can only be defeated by lighting one of the torches in the room with Magic Powder; doing so will weaken them and turn them dark as they flee in defeat. At this point, Link can strike them with his blade to destroy them, or wait until they have left, upon which point the chest containing the Power Bracelet will appear.

Trivia

 * Using light to weaken or defeat enemies occurs in many later Zelda games. A number of enemies, such as ReDeads and Nocturn (a very similar ghost enemy), can be defeated in this way.

Nomenclature
Boo Buddy's Japanese name, Teresa, comes from the Japanese word, meaning "to be shy", fitting their bashful nature.