Adventure Time returns on Friday the 21st of April when Orbs will be airing. The following week a new mini-series titled "Elements" is scheduled to air. The usual two episodes a night for four nights.

List of episodes:
Skyhooks
Bespoken For
Winter Light
Cloudy
Slime Central
Happy Warrior
Hero Heart
Skyhooks II

This mini-series will be about what Fern was doing during Islands.

http://tvlistings.zap2it.com/tv/adventure-time/episode-guide/EP01246265?aid=zap2it

The schedule can always change these listings are not final and no official word has been put out from CN.