Metroids are fearsome, flying parasites resembling jellyfish. The Metroid was discovered on the Planet SR388 in suspended animation, but was revived after 24 hour exposure to beta rays. On the return voyage to the Galactic Federation Headquarters, the GF starship was intercepted by Space Pirates who murdered the crew and stole the Metroids for reproduction as biological weapons.
Metroids latch onto their prey with incredible strength, making them nearly impossible to dislodge. While attached, they completely drain the life energy of their prey, leaving the mummified remains. They can only be removed by freezing the creatures or with the force of an explosive blast, techniques that are usually fatal to the victim. Their gelatinous shells reflect and absorb nearly every kind of attack, leaving them invincible to conventional weaponry.
Metroids will grow in size after consuming large amounts of energy. If enough energy is consumed, they will reproduce through mitosis, splitting into two. Metroids will also split if exposed to beta rays for a period of 24 hours. Their rapid reproductive cycle and the fearsome speed with which they consume their prey make them one of the most dangerous life-forms in the cosmos, potentially capable of destroying all of galactic civilization.