Name the Cory
Yes that is a yoyo loach, they grow to 6" long and get very fat. They are really social fish and should be kept in groups, and they can indeed be aggressive. I got a pair of them, very small like yours. During the time I had them I had a beta, 2 White Cloud Mountain minnows, and 3 neon tetras mysteriously disappear. Usually just one or 2 fish each night. I only saw a couple carcasses. I returned the loaches and these disappearances stopped.
20 gallon high-tech planted