Black Earth Master

Spellcasting. The master is an 11th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 17, +8 to hit with spell attacks). It knows the following sorcerer spells (an asterisked spell is from appendix B):

Cantrips (at will): acid splash, blade ward, fire bolt

1st level (6 slots): earth tremor,* expeditious retreat, shield

2nd level (5 slots): misty step, Dragon's Breath, Earthbind, 

3rd level (4 slots): Counterspell, Dispel Magic, Erupting Earth

4th level (3 slots): Polymorph

5th level (2 slots): Wall of Stone

Master of Concentration.  The Black Earth Master can concentrate on two spells when at least one of those spells is transmutation magic.  Damage does not cause the Black Earth Master to lose any concentration on magic of the school of transmutation.

Multiattack Surge. The master makes three melee attacks.

Warhammer, +2. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 7 (1d10 + 12) bludgeoning damage.

Unyielding. When the master is subjected to an effect that would move it, knock it prone, or both, it can use its reaction to be neither moved nor knocked prone.