Waiting Room's unlock notice.
An unlockable stage is a stage in the Super Smash Flash series that is not available at the start of the game (unlike a starter stage), but must be unlocked. Like an unlockable character, it is required to accomplish a particular in-game feat and once completed, a notice will be shown, telling the player that the stage has been unlocked.
In Super Smash Flash
| Stage | Universe | Criteria |
|---|---|---|
| Battlefield | Super Smash Bros. | Clear All-Star with any character. |
| Final Destination | Super Smash Bros. | Unlock all characters. |
In Super Smash Flash 2
| Stage | Universe | Criteria | |
|---|---|---|---|
| Devil's Machine | EarthBound | 
|
With Ness's eleventh costume, self-destruct three times in a Group match. |
| Final Valley | Naruto | 
|
Clear event #12: Shadow Clone Showdown. |
| Hyrule Castle | The Legend of Zelda | 
|
Complete Classic with Link, Zelda, or Sheik on Normal difficulty or higher without using any continues. |
| Krazoa Palace | Star Fox | 
|
Clear Crystal Smash in under one minute. |
| Meta Crystal | Super Smash Bros. | 
|
Complete Classic on Hard difficulty or higher without using any continues. |
| Mushroom Kingdom | Mario | 
|
Complete Classic for the first time. |
| Saffron City | Pokémon | 
|
Complete Classic with Jigglypuff. |
| Sky Pillar | Pokémon |
|
Release Jirachi from a Poké Ball or Master Ball in a Group match. |
| Steel Diver | Steel Diver | 
|
Get a total of 20 KOs or self-destructs in the bottom blast line on Gangplank Galleon, Lake of Rage, Fairy Glade, or Planet Namek. |
| The World That Never Was | KINGDOM HEARTS | 
|
Clear event #21: Battle of the 99 Heartless?. |
| Urban Champion | Urban Champion | 
|
Complete Classic with a score of 550,000 points or higher. |
| Waiting Room | Super Smash Bros. |
|
Play any Group match with Sandbag participating. |
| World Tournament | Dragon Ball | 
|
Play 15 Group matches, or complete Classic with Goku on Hard difficulty or higher without using any continues. |
In demo versions
These stages were made unlockable when first introduced in their respective demo versions:
| Stage | Universe | Criteria | Version | |
|---|---|---|---|---|
| Chaos Shrine | FINAL FANTASY | 
|
Unlock Black Mage. | 0.7 |
| Clock Town | The Legend of Zelda |
|
Clear Break the Targets with all 19 starter characters and accumulate a total best time of less than 5 minutes. | 0.8 |
| Sand Ocean | F-ZERO | 
|
Win 10 Group matches as Captain Falcon. | |
| Desk | Chibi-Robo! | 
|
Clear event #26: Cleaning Duty. | Beta 1.0.0 |
Gallery
Unlock notices in Super Smash Flash 2
Devil's Machine's unlock notice.
Final Valley's unlock notice.
Hyrule Castle's unlock notice.
Krazoa Palace's unlock notice.
Meta Crystal's unlock notice.
Mushroom Kingdom's unlock notice.
Saffron City's unlock notice.
Sky Pillar's unlock notice.
Steel Diver's unlock notice.
The World That Never Was's unlock notice.
Urban Champion's unlock notice.
World Tournament's unlock notice.
Early designs
Chaos Shrine's unlock notice.
Sand Ocean's unlock notice.
Clock Town's unlock notice.
Metal Cavern's early unlock notice, before being renamed to Meta Crystal.
World Tournament's early unlock notice, mistakenly displaying the tagline for Final Valley.