Metroid 2: Return of Samus — is a side-scrolling action-adventure game in which the player controls the protagonist Samus Aran on the fictional planet SR388. Players progress through the game by using Samus' weapons to kill a fixed number (47) of Metroid creatures. The player is given a detector that shows the number of Metroids remaining in the area. Once all the creatures are destroyed, an earthquake occurs and the lava level on the planet drops, allowing Samus to travel deeper through its tunnels. Metroid creatures are found at different evolutionary stages of their development cycle: original, alpha, gamma, zeta and omega. The more developed the organism, the stronger its attack.