Innate Spellcasting: Witherhead's spellcasting ability is Charisma (spell save DC 17). Witherhead can innately cast the following spells, requiring no material components:

Cantrips(at will): Chill Touch, Vicious Mockery
1st level(3 slots): Command, Thunderwave
2nd level(2 slots): Hold Person, Spike Growth

Witherhead will cast Spike Growth when enemy's enter the room.
Witherhead will cast Thunderwave when enemy's come in melee range.

Multiattack: Witherhead can attack twice every turn. This includes spells.

Longbow ranged weapon attack: +6 to hit, range 50/300ft., one target. Hit: (2d8 + 3)
Arrowstorm ranged weapon attack: +6 to hit, multiple targets. Hit melee range: (6d8 + 3), hit medium range: (3d8 + 3).
If Arrowstorm is used while the target is within melee range, witherhead has advantage on his attack roll.

As a bonus action he can summon Witherhead spawns to help him in battle.