The creature becomes Incorporeal: it cannot make weapon attacks or be physically harmed.   It has resistance to all damage from nonmagical sources, and it cannot be targeted by nonmagical attacks or effects.   It still takes full damage from spells and magical effects.   It is considered to be under the effects of Sanctuary (save ends) against creatures it hasn’t harmed. Spells that target the creature while banished have advantage on attack rolls and impose disadvantage on its saving throws, Spells against target deal double damage.