The Adjudicator was added as part of the Dark Forest makeover.
This master of the Woodland Mansion is no easy fight.
The Adjudicator meditates in his study within the Woodland Mansion.
Attacking him or placing/breaking any blocks will cause him to wake, beginning his boss fight.
Leaving his boss room will cause the fight to end and the Adjudicator will return to his meditation and begin healing.
During the fight he will summon enemies, teleport around and attack you with a variety of weapons - so be prepared.
When killed Rootlings will drop: