Rifick, an avid Super Smash Bros. stage builder who's made some of the coolest custom levels I've seen for the game, just posted a handy tutorial for some of the mode's trickier parts. Give it a look if you've been having any problems with your own custom stages. And let me know if you have any other tips too!
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Is there a way to build a usable ladder? 'Cause that option was in Brawl.
I'll take a look at the guide anyway as I'm really into creating my own stuff in games.