I've never completed the fish and sea creature collections. Unlike bug catching, you don't know what you're getting until you reel it in or dive for it, which is why I just do bug catching instead.
never played the stalk market (so I could never get all the badges even if the streetpass one wasn't impossible), just too tedious. Also never did the last HHA challenge to get the weird red/gold house exterior or whatever. And I almost never unlocked Katrina because I didn't realize that was even possible until I saw her shop in my brother's town lol I neeveeerrr visited her tent when she was in town cuz I had a lovely phone.