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 either have the same (albeit remixed each time) music track, titled Escape!, or Ridley's theme is used. Metroid Prime and Metroid Prime Hunters have had original music tracks though.

To date, Metroid II: Return of Samus is the only game in the series to not feature a Countdown. Instead, Samus leaves Phase 9 with the Baby carving out obstacles for her.

Metroid
In Metroid, upon defeating Mother Brain, Samus is given 999 time units, (3 units is one second, therefore the time limit would be 333 seconds, or about 5 1/2 minutes) to climb up a tall, tower-like room to escape from Zebes.

Super Metroid
Super Metroid has two countdowns, one at the beginning of the game and one at the end. In the beginning, Samus must evacuate Ceres Space Colony in less than one minute following her battle with Ridley. At the end of the game, Samus has six minutes to escape from Zebes as the planet begins to explode (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 in under one minute. In the final sequence, Samus has three minutes to escape the research station whilst it hurtles toward SR388 while fighting an Omega Metroid. This is the first Countdown ever to have a boss included.

Metroid Prime
In Metroid Prime, Samus must escape the Space Pirate frigate Orpheon in seven minutes, 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: Zero Mission
In Metroid: Zero Mission, after defeating Mother Brain, Samus must escape from Tourian in three to one minute(s), depending on the difficulty, by jumping onto various crumbling platforms, similar to the original Metroid. Later, Samus must evacuate the Space Pirate Mothership under five to two minutes after defeating Mecha-Ridley.

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 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. Also, when Samus enters the Fuel Stack for the first time during her second visit to the Vesper Defence Outpost, there is a malfunction with the power generator that threatens to destroy the entire station. Samus must get to the top of the room in one minute and fix the problem by scanning a computer in an alcove.

Metroid Prime 3: Corruption
In Metroid Prime 3: Corruption Samus must get to the Control Tower before the Leviathan hits Norion in four minutes. Also, she must activate an escape pod in SkyTown to escape the Spire that is dropping on the Leviathan's shield after she shuts off the pod's engines. Neither countdown actually depicts a timer on-screen, as a computer voice tells Samus every minute, unlike the rest of the series.


 * While not exactly indicated on the HUD, a timer does show when on the spire. After killing all the Space Pirates and opening the repair hatch below the escape pod, if Samus looks at the screen she used to shut down the engines, a countdown can be seen on the screen.


 * While not exactly a "countdown," there is also a time limit on the boss fight against Meta 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.

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 lose one stock. Warning Siren plays in this segment.

Super Smash Bros. Brawl
In Adventure Mode: The Subspace Emissary mode of Super Smash Bros. Brawl, there is a countdown during the escape from the Isle of Ancients. Several Subspace bombs are set to go off, and the characters must escape the facility (at this point there is no countdown; the screen automatically scrolls, killing the player if he/she falls behind). Once the player exits the chamber, the player must defeat Meta Ridley whilst on top of the Falcon Flyer in less than 2 minutes.

Trivia

 * Countdowns are likely inspired by similar escape sequences in the films Alien and Aliens, which gave much inspiration to the Metroid series. The escape sequence of Aliens is also similar to that of Metroid Fusion, where the female protagonist is stranded with no means of escape and a dangerous specimen cornering them, and at the last minute, the gunship flies in to save them. This countdown is also similar to the escape sequence in Alien Resurrection, where the protoganist must escape a research vessel before it crashes into the planet below.