From the Super Mario Wiki
Rams are enemies that Wario faces in Wario World, appearing in Beanstalk Way. They are rams, as their name implies, with light brown fur and long horns.
Rams are very weak defensively, but are offensive forces to be reckoned with. Rams can be stunned with only a few punches, but when angered, leap and crash down on Wario, horns first. Once stunned, a Piledriver, Wild Swing-Ding, or Power Throw will defeat them.
Rams are also found stampeding down mountains in infinite numbers in Beanstalk Way, fulfilling the same role as Shivering Mountains' Skiing Yetis. They cannot be defeated in this state.