Cards 30 / 30
Ready Spells (7)
Summon Blood Puppet
Pick two of the following: Summon Dread Wraith, Sonic Swordsman, Leech Warrior, Devotion, Cut the Strings, Sword of Virtue
String Mage is an incredibly versatile unit. I have no doubt that she can be used to great effect with some kind of crazy status token manipulation engine, but today we're doing something a bit more...sanguine.
The big synergy here is between String Mage and Small Sacrifice. Using both, you get two instances of "deal 1 damage to a target unit" at the incredibly low cost of [[main]] - [[side]] - [[ceremonial:class]]. That's a brutal amount of board control, especially if you manage to assemble all 3 copies of SS. String Mage is also incredibly effective with Blood Puppet - if your opponent pays valuable dice to damage them, you can respond by moving that damage back onto to String Mage.
Your primary win condition is board control. The String Sacrifice combo offers strong, cheap removal while Blood Puppets slowly kill the opponent. There are a bunch of First Five options that help expand on this - Cut the Strings works both as a counter to Reflections in the Water and a slightly clunkier extra Small Sacrifice; Sonic Swordsman outputs a ton of extra damage; and Sword of Virtue is pretty effective against just about everything.
The main reason I chose Odette Diamondcrest is because 9 times out of 10, I will be guarding my String Mage with my Phoenixborn, and using Odette's Retribution helps us control the board further and supply more options for String Mage. I also like Sword of Virtue as a swiss army knife solution to most of your problems.
That being said, almost any Phoenixborn will work here, you just need the main combo and mostly Ceremonial/Sympathy deck. Since your battlefield number isn't as important, you can find plenty of success with Lulu Firststone's special card Phoenix Barrage, or Coal Roarkwin's slash ability.
I chose Dread Wraith as a solid finisher due to it's excellent synergy, but you might do better with Mirror Spirit due to its amazing ability to close out a match and effectively suppress blockers (also because you have lots of ways to kill the useless ones)