It's not every day Ellie meets a hitherto-unclassified species of pokemon. With the modern pokedex and the internet and so forth, barring some obscure evolutionary criterion or underexplored region's variant form, there's generally enough data floating around to at least type anything you might meet with a simple scan.

Which is what makes this mirror-headed snake creature so unusual. Also the way it attacks Ellie immediately, without any sort of posturing. She doesn't have time to do more than reach for one of the balls at her belt before she is engulfed.