Rick and Morty is a series that is very popular right now. Those who have just started to watch would like to watch episodes from its first season. Some videos are available at adultswim.com. You can look for a video downloader online that will help you get the videos from the website and download to your device.
If in case adult swim does not allow this, there are other websites online that will provide you with this option. There are also some applications that will enable you to stream the videos, but this may not be what you want since you like to watch the episodes when you are offline.