Dragonfly Lilypads are an open-air dungeon found in large water bodies within Submerged Swamps. They are made out of Giant Lilypad Blocks and white Petal Blocks, and have some Vines on the sides to assist with climbing out of the water.
In the centre of the flower structure, there is a Dragonfly spawner. These spawners are currently slightly glitchy, and drop Ender Pearls when broken, although this may be an allusion to a certain variety of Dragonfly (Hint: Why Ender Pearls?).
Beneath the spawner sits a Chest filled with Erebus dungeon-tier loot.
These dungeons are particularly tricky for inexperienced Erebus adventurers as Dragonflies can spawn suddenly and carry the player away from the lilypad.