Anything is possible. It just depends on your commitment. I'd think making anything that could match Terraria in the App Store would be difficult. It'd require a lot a lot of work, and would probably be one of the biggest projects ever done in GameSalad. I'd suggest starting small, and building up. Minecraft and Terraria both took very skilled professional developers hours and hours of work to make great.
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I made this in GS a while ago: