Buulgari, Death Slaad

Shapechanger. The slaad can use its action to polymorph into a Small or Medium humanoid, or back into its true form.  Its statistics, other than its size, are the same in  each form. Any equipment it  is  wearing or carrying isn't transformed. It  reverts to  its true form  if it dies.
Innate Spellcasting. The slaad's innate spellcasting ability is  Charisma  (spell save DC 17, +9 to hit with spell attacks). The slaad can innately cast the following spells, requiring no material components:

At will detect magic, detect thoughts, [Tooltip Not Found] (self only), mage hand, major image
2/day each: fear, fireball, fly, tongues
1/day each: cloudkill, plane shift
Magic Resistance. The slaad has advantage on saving throws against spells and other magical effects.
Magic Weapons. The slaad's weapon attacks are magical.
Regeneration. The slaad regains 10 hit points at the start of its turn if it  has at least 1 hit point. 

Multiattack. The slaad makes three attacks: one with its bite and two with its claws or greatsword.
Bite (Slaad Form Only). Melee Weapon Attack: +11 to hit,  reach 5 ft.,  one target. Hit: 11 (1d8 + 9)  piercing damage plus 7 (2d6) necrotic damage.
Claws (Slaad Form Only).  Melee Weapon Attack: +11 to hit, reach  5 ft., one target. Hit: 12 (1d10 + 9)  slashing damage plus 7 (2d6)  necrotic damage.
Greatsword. Melee Weapon Attack: +11 to hit,  reach  5 ft., one target. Hit: 12  (2d6 + 9)  slashing damage plus 7 (2d6) necrotic damage.