The monumental success of the Pokémon franchise has spanned multiple generations, so you can bet that the cartoon has inspired more than a few imposters. Whenever a series becomes popular, other aspiring franchises leech onto it in an attempt to siphon out the qualities that made the original show such a goldmine. Sometimes, a particularly well constructed knockoff will succeed in gaining its own fan base, but most just end up feeling like desperate Pokémon copycats.
Blatant Pokémon ripoffs exist in all forms of media; other anime series regularly crib the "kids training monsters to fight in tournaments" formula, and more than a few video games have copied the franchise's signature practice of releasing two complimentary games in tandem. The shows that copied Pokémon prove that while imitation might be flattering, it definitely doesn't guarantee success.