Bertholt here will more than likely hang behind whoever he ends up hanging around in the mansion. Because he hasn't been here long, he won't be as torn up over the loss of his pokemon but he'll still make it a priority to get it back once he gets over the initial shock of ending up in another weird location. At least he only lost one!

As far as monsters go? He'll be trying his best to steer clear of them but in general they'd be similar to the big bads from his world.