I believe this is 99.9% sure to be a real Pokemon, and our first glimpse into Gen 8!!
It's quirky and cute and super tiny! Definitely one of the smallest (if not the smallest) Pokemon I've ever seen in the PoGO overworld, which I'm sure is an intentional reflection of its actual size.
I know what the skeptics may be thinking reading this post: it could just be a "fake" -- simply one of Niantic's little placeholders. However, at the moment, there's no real evidence to suggest that it is.
"Well then, OVERGRO, what's the evidence that it's real?"
I would say the evidence is past patterns -- sure, this particular stunt is unprecedented, but overall, Gamefreak/Pokemon doesn't troll around, especially when it comes to revealing new Pokemon. It would be totally out of character for Gamefreak to give the green light to Niantic to hype up a new creature this much without there being an obvious marketing basis beyond just directing media attention to PoGO and Pokemon in general.
Despite my general disdain for PoGO seemingly driving the casual-ization of the main games, I still respect the huge impact it has had, and continues to have, on the series as a whole. Its reach is unlike anything else. Years later, I still consider it a phenomenon (and rightfully so, with active player count this summer being the highest its been since launch).
Popping our nutty, blobby little friend out into the world (the real world at that) around the time of a PoGO special event (the Community Day) was such a fresh, intriguing, and bizarre way to reveal the first Pokemon of a generation that is still 12-15 months away. Perhaps it was an obvious idea in retrospect, but I think it was a well done one nonetheless!