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Pokemon was a one-off hit. It was in the right place at the right time, and since then the designs, marketing, brand recognition and the humongous media variety (cards, anime, etc) have taken care of keeping it relevant.
Pokemon ripoffs "failed" because they expected to directly compete with the games, without realizing that the franchise is what's keeping the games relevant, not the games themselves, for most people but the smallest group of "core" players. You can't not "fail" in this sense without doing what yokai watch did: create a whole media franchise, but they failed in not bringing it around the world, and even if they did they'd have to do things pokemon has never done in hopes to trigger a new pokemania or pokemon go craze.
If you make your own thing, make your own thing. Take the elements of pokemon you like and combine them with unrelated elements to make a game you are happy with. Don't bother appealing to a fanbase that plays pokemon because it's popular.