Other than a time-trial mode (which seems to be a 'Flow Free' innovation, so I'm disinclined to copy that outright) and sprite-themes ('halloween pack' instead

Other than a time-trial mode (which seems to be a 'Flow Free' innovation, so I'm disinclined to copy that outright) and sprite-themes ('halloween pack' instead of letters from the alphabet), I can't think of much at the moment. I don't know about hints being a core feature though. Flow Free includes as many as 600 free levels but only 3 free hints. It could be that they are monetizing poorly on level packs, relative to downloads, and hoping to catch up with hints.