Jellybeams are jellyfish-like enemies that appear in New Super Mario Bros. Wii. They are rare, only appearing in 8-4. They light up the water surrounding them, and attack Mario, Luigi, Yellow Toad, or Blue Toad by touching one of the characters. They can still light up the water if frozen.
The Jellybeam's name is a pun on jelly, referring to their jellyfish-like appearance, and beam, referring to the beam of light that comes from them.
Their name may also be a pun on jellybean, the candy.