Just to make sure, you, the player, get to choose your items right? If so than here's what I would do:

Race: Yuan-Ti


Class: Moon Druid 20


Stats:

Str: 10

Dex: 14

Con: 14

Int: 10

Wis: 22

Cha: 12


Feats:

Alert

Heavily Armored


Items:

Scorpion Armor

Staff of Fire

Boots of Striding and Springing

+3 Shield, or that shield that gives +2 to Initative

Book that Boosts Wisdom by 2


Your main strategy here is to go first, and with Alert, Scorpion Armor, and potentially the shield you have a +14 to Initiative. Afterwards, pop off a spell that you can retarget every round, turn into an Elemental, and either dive underground or fly into the sky to avoid damage.

Alternatively, you can take an 18 Wisdom, boost it to 20 with the book, and grab Mobile on top of the other two feats