Yep! That's a Zergoose. I am kinda mad though. I was about to take a Dragonwhmsy egg a few days ago and someone just stole the thing as I tried to click it. I was outraged! I wanted something rare too...
EDIT: Professor Elm... check!
Like I said earlier, it's a very rare item that you get through underground. I am currently trying to get more, so I'm going back and forth between Professor Badges and the Thunder Badge.