Hardest things to program in a platformer Mario game?

[SuperSledgeBro]

I've been unsucessfully trying to get a good platform engine working right. Making simple things like walls, solids, jump-through platforms, powerups and such is no problem for me at all. But, like you, I struggle a lot with moving platforms. My engine will not be perfect if it doesn't have platforms that can go through each other without causing weird behavior. I'm still trying to find a good collision system...

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