Volo's Guide to Monsters (5e)
Spellcasting. The archdruid is an 18th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 17, +9 to hit with spell attacks). It has the following druid spells prepared:
Scimitar. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) slashing damage.
Change Shape (2/Day). The archdruid magically polymorphs into a beast or elemental with a challenge rating of 6 or less, & can remain in this form for up to 9 hours. The archdruid can choose whether its equipment falls to the ground, melds with its new form, or is worn by the new form. The archdruid reverts to its true form if it dies or falls unconscious. The archdruid can revert to its true form using a bonus action on its turn.
While in a new form, the archdruid retains its game statistics & ability to speak, but its AC, movement modes, Strength, & Dexterity are replaced by those of the new form, & it gains any special senses, proficiencies, traits, actions, & reactions (except class features, legendary actions, & lair actions) that the new form has but that it lacks. It can cast its spells with verbal or somatic components in its new form.
The new form's attacks count as magical for the purpose of overcoming resistances & immunity to nonmagical attacks.
Any Climate; Any Terrain, prefers Forest, Mountain, & Swamp