This is the most common way to say goodnight to a group of people in Japanese. It literally means "please have a good night's sleep."
おやすみ (oyasumi)
This is a more informal way of saying goodnight. It can be used with friends or family members.
いってらっしゃい (itterasshai)
This phrase is used to say goodbye to someone who is leaving. It literally means "go and come back safely."
お元気で (ogenkide)
This phrase is used to wish someone well when they are leaving or going on a journey. It literally means "stay healthy."