Some people are reacting strongly to this pokemon and hey that’s fair, but there is a really interesting reason for why this pokemon exists.
Back in the 1800′s people who weren’t native to Hawaii came over to set up sugar cane plantations and with them came the thing that comes with every traveling conqueror. Rats.
These rats were a Huge problem and caused a lot of destruction. Eventually someone had the bright idea that since mongooses eat small mammals (and anything they can get their small teeth on) they would be and excellent way to take care of the rodent problem.
So the plantation owners brought them to the island, patted themselves on the back for being very clever, and thought their problems to be over.
Rats are nocturnal and mongooses are diurnal.
They hardly interacted at all. So instead of getting rid of one pest there was now two destructive organisms to deal with (And many more invasives to come). In Hawaii today, mongooses prey upon endangered birds, sea turtle eggs, and all sorts of little critters. They generally cause a lot of trouble.
Back to this pokemon in particular, on top of being a mongoose this pokemon is categorized as the “Loitering Pokemon”. It hangs around without a real purpose and people generally don’t want it to be there. Could this pokemon’s offsetting appearance be intentional? Maybe. It’s biologically destructive history would be easier to ignore if it was cute.
One thing that can be said for certain is that since Yungoos is around, it is likely that rattata will be in the Alola region as well.