Overview
Here’s how to unlock all the characters, stages, palettes, and more in the Showdown mode with minimal effort and quick(ish?)
The nitty gritty
1. Go into the battle menu.
2. With two controllers, select your characters. (Keyboard is okay, but I think only one player on the keyboard is supported)
3. Before you enter the stage select, be sure to go into the match options and set the following:
Game type: Showdown
Time Limit: Unlimited
Stock: 1
Stage choice: Whatever you want
…and everything else off. (Gem goal can’t be changed in Showdown mode.)
4. Start the game!
5. Wait 510 minutes… (During this time, you might want to do something else…)
NOTE: To check the progress of the unlocks, pause the game, go into the unlockables menu and press select. You can see how many minutes you spent in multiplayer in the top-right.
6. Once the 510 minutes are over, kill the other player and brace for the many unlock screens. (I’ve never exited a match, I’ve always killed the other player. EXITING MAY NOT WORK! If you don’t unlock anything by exiting, then don’t say I didn’t warn you!)
7. You now have everything yay!