Whisp

The Whisp, sometimes spelled Wisp and also known as Anti-Fairy, is a recurring enemy in the Zelda games. First seen in A Link to the Past, as a variation of the Bubble enemy, they are skulls ringed by red or blue flames.

A Link to the Past and Four Swords Adventures
In A Link to the Past and Four Swords Adventures, Whisps are referred to as Anti-Fairies, which, as their name implies, are the exact opposite of a healing fairy in that it saps the victim's physical health, and in some cases their magical energy too. In his quests, Link discovers that he can use Magic Powder to turn the specter into a fairy, healing him in the process, suggesting that an Anti-Fairy is a fairy corrupted by some sort of dark magic.

The Cloud enemies are corrupted versions of Anti-Fairies.

Link's Awakening, Oracle of Ages and Oracle of Seasons
In Link's Awakening, Oracle of Ages, and Oracle of Seasons, it is called Whisp. It moves in diagonal patterns and can be defeated with a single hit from Link's Boomerang. Curiously, defeating a Whisp in Link's Awakening never results in pick-ups, such as recovery hearts and Rupees, but will result in a Fairy for Oracle of Ages, and Oracle of Seasons.

The Minish Cap and Four Swords
In The Minish Cap and Four Swords, the Wisp is an enemy which is similar to the Blue Bubble: it will jinx Link if it touches him, however it is non-agressive and will simply float around. The sword does not affect them but the Gust Jar can be useful.