An unlockable stage is a stage that is not available at the beginning of the game, unlike a starter stage, but must be received through other means.

In Smash 64, the game did not use placeholders for unlockable stages. In Melee, this was the only installment which used placeholders for unlockable stages. The only unlockable stages which appeared as placeholders was Mushroom Kingdom II, Brinstar Depths, Fourside, Big Blue, and Poké Floats. The other 6 unlockable stages (Flat Zone, Past Stages, and Special Stages) did not appear as placeholders. The placeholder slots were removed in Brawl, Smash 4, and Ultimate.

Super Smash Bros.

Stage How to Unlock
Mushroom Kingdom Clear 1P Game with all 8 starter characters and play each starter stage in Vs. Mode at least once.

Super Smash Bros. Melee

Stage How to Unlock
Battlefield Clear All-Star Mode with any character.
Big Blue Play 150 VS. matches.
Brinstar Depths Play 50 VS. matches.
Dream Land N64 Complete Target Test successfully with all 25 characters.
Final Destination Clear Event 51: The Showdown.
Flat Zone Complete Classic Mode with Mr. Game & Watch.
Fourside Play 100 VS. matches.
Kongo Jungle N64 Complete 15-Minute Melee with any character.
Mushroom Kingdom II Obtain the Birdo trophy.
Poké Floats Play 200 VS. matches.
Yoshi's Island N64 Hit more than 1312.3/400m in Home Run Contest with Yoshi

Super Smash Bros. Brawl

Stage How to Unlock
75 m Play as Donkey Kong 20 times on Vs. Mode.
Big Blue Play as Captain Falcon 10 times on Vs. Mode.
Flat Zone 2 Unlock Mr. Game & Watch.
Green Greens Play as Kirby 20 times on Vs. Mode.
Green Hill Zone Unlock Sonic.
Hanenbow Clear the "Flower Blooms in the Echoes" event.
Jungle Japes Play on any Melee stage 10 times in Vs. Mode.
Luigi's Mansion Play as Luigi 3 times in Vs. Mode.
Mario Bros. Clear the "Wario Bros." event.
Pirate Ship Unlock Toon Link.
Pokémon Stadium Play on Pokémon Stadium 2 10 times in Vs. Mode.
Spear Pillar Clear "The Aura Is With Me" event.

Super Smash Bros. for Nintendo 3DS

Stage How to Unlock
Balloon Fight Play as Villager 3 times in Smash.
Dream Land Use a Final Smash while playing as Kirby.
Flat Zone 2 Unlock Mr. Game & Watch and complete the first Challenge panel.
Magicant Unlock Ness.
Mute City Win 3 Smash battles with Captain Falcon.
Pac-Maze Use a Final Smash twice while playing as Pac-Man
WarioWare, Inc. Unlock Wario.

Super Smash Bros. for Wii U

Stage How to unlock Golden hammer
Duck Hunt KO at least one opponent in a single Solo Cruel Smash. Not allowed
Flat Zone X Play alone as Mr. Game and Watch and destroy 100 or more blocks in a single game of Trophy Rush. Not allowed
Kongo Jungle 64 Clear the event “The Original Heavyweights”. Allowed
Pac-Land Play on all three maps in Smash Tour. Allowed
Pokémon Stadium 2 Clear the event “When Lightning Strikes”. Allowed
Smashville Clear the event “Playing Tricks”. Allowed

See also