Countdown

Countdowns have long been the signature of the Metroid series (every game except Metroid II: Return of Samus has at least one). Often, after defeating the final boss, Samus must evacuate the location in a certain time. Six minutes is a very frequent time limit, though three minutes and one minute have been known to appear as well. They often have the same, (albeit remixed each time) music track.

Metroid
In Metroid, upon defeating Mother Brain, Samus is given 999 time units, (3 units=one second, therefore the time limit would be 333 seconds, about 6 minutes) to climb up a tall tower-like room to escape from Zebes.

Super Metroid
In Super Metroid, Samus must evacuate Ceres Space Colony after Ridley flees the station. Then, at the end of the game, Samus has six minutes to escape from Zebes as the planet begins to explode (ironically, one of the passages is the original tower room from Metroid).

Metroid Fusion
There are many countdowns in Metroid Fusion. The first countdown happens in Sector 3, where Samus must race to the Main Boiler Room to stop the Biologic Space Laboratories research station from overheating and exploding in six minutes. Later, Samus must Space Jump to the top of a shaft with Metroids floating around her under one minute. In the final sequence, Samus has three minutes to escape the research station whilst it hurls toward SR388.

Metroid: Zero Mission
In Metroid: Zero Mission, after defeating Mother Brain, Samus must escape from Tourian in two minutes by jumping onto various crumbling platforms, similar to the original Metroid. Later, Samus must evacuate the Space Pirate Mothership under five minutes after defeating Mecha-Ridley.

Metroid Prime
In Metroid Prime, Samus must escape the Space Pirate frigate Orpheon before it explodes at the beginning of the game.

Retro Studios stated in an interview that a timed escape was planned for the end of the game, but they didn't want to delay the game another month for it.

Metroid Prime 2: Echoes
At the final sequence of Metroid Prime 2: Echoes, after taking the last of Dark Aether's energy and defeating the Emperor Ing, Samus must defeat Dark Samus and return to Aether whilst Dark Aether crumbles from loss of energy, in 8 minutes.

Metroid Prime 3: Corruption
In "Metroid Prime 3" Samus must get to generator B before the Leviathan hits Norion in four minutes. Also, she must activate an escape pod in SkyTown to escape the the spire that's dropping on the Leviathan's shield.


 * While not exactly a "countdown," there is also a time limit on the boss fight against Ridley in Metroid Prime 3: Corruption; this, however, is measured in meters (representing the distance between Samus and the bottom of a shaft) rather than in actual time.

Metroid Prime Hunters: First Hunt
Two of the training exercises in Metroid Prime Hunters: First Hunt include countdowns. Regulator has a very large 10 minute time-limit, while the Morph Ball mode ends at 55 seconds if the player does not collect the last module before then.

Metroid Prime Hunters
In Metroid Prime Hunters, Samus must escape from each planet/station after defeating one of the 2 types of bosses and acquiring an octolith. The time limit differs for each boss encounter, ranging from 8 minutes, 30 seconds, to 2 minutes.

Super Smash Bros. Melee
In the Adventure Mode of Super Smash Bros. Melee, the player must escape an exploding Zebes in 40 seconds after fighting Samus. If the player succeeds, they earn a Samus's Gunship trophy. If they fail, they loose one stock.