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As a Rotom Enjoyer, I'm actually thrilled that its become more of a mascot. Surprisingly though, there's not a TON of merch all things considered, even though the phone/dex are pretty integrated into the series now. It is nice to see more base Rotom stuff (Whats Your Charm Point? line of merch in Japan feature him as the most recent release!)
Rotom is actually Ishihara's favorite Pokemon, and probably a big reason why it's gotten a bit of a push (consider, probably why Poliwhirl was pushed in the US at the beginning of Pokemania)
As for Rotom being unique- I think originally it was designed to be some kind of legendary/one of a kind Pokemon. It uses the Legendary encounter music in DP, and an old Pokemon mailbag letter did specifically say it was Legendary, but that's totally been retconned. Charon's story still works as he was the first to DISCOVER Rotom and name it, but every piece of Pokemon media implies there are more (and they do the same with Legendaries anyways so the point is moot)
