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 15, +7 to hit with spell attacks). The slaad can innately cast the following spells, requiring no material components:

At will: detect magic, detect thoughts, invisibility (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.

Actions

Multiattack.

The slaad makes three attacks: one with its bite and two with its claws or greatsword.

Bite (Slaad Form Only).

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) piercing damage plus 7 (2d6) necrotic damage.

Claws (Slaad Form Only).

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 10 (1d10 + 5) slashing damage plus 7 (2d6) necrotic damage.

Greatsword.

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) slashing damage plus 7 (2d6) necrotic damage.

Death Slaad