I left out memory challenges because a good number of them exist in this arcade plus there are some games with memory challenges within other games, such as one slot game I'm fond of (forget the name). One that poses a major memory challenge is Bees Saal Baad, named for a movie in India of the same name whose plot involves long lost twins...so yeah, it's a matching memory game, but with a good many different pairs, which is what makes it challenging. But beware of buggy versions, and there are a few; one locks up in the last level when you click on one image and it doesn't recognize the fact that you clicked the matching image. The only one I know where to play this is at the previously mentioned Next Level Arcade but that one is set to time out WAY too soon, one never reaches the last level, and I expect it's because I reported the bug that happens at the last level. Can't even get to the next-to-last level there either.