Green Bubble

The Green Bubble appears in various dungeons throughout Ocarina of Time & Majora's Mask. They float in a set pattern, with their green flames acting as a barrier. To defeat them, simply wait until their flames die down and take that as a chance. They won't attack you directly, and so can be considered easier than most. They usually appear in groups of two

One appears floating around the water way in the Kakariko Well mini-dungeon. This one is larger than usual, but still as easy to kill.