If you accept a suggestion: Divinia is a solid option to use as she can fill both roles of offering Support with Buffs, Cleanse and Healing as well as generating mana by exploding gems. All of it with a single troop and you can maybe (or have already) pull her in Event Keys this week since she is from Dragon’s Claw.
I don’t know which weapons you have, but a rather ok one that every player will have eventually is Death Knell:
It wouldn’t interfere much with Divinia and Mistralus manas and the Damage plus extra turn allows you to keep casting spells and keep matching gems.
And it’s great when you land in a scenario where you can use a spell with your hero or Mistralus gaining an extra turn, matching 4/5 gems and then enchant everyone and still keep playing and keep storming the enemy with spells.
For the Tanker I would suggest:
He blocks another color for Mistralus, and with Divinia your Mythic would have only Brown Mana free to fill her, but since Dwarven Gate provides 5 Mana to all other allies on cast you are not missing blue matches completely. It also provides Barrier which is just great. It’s a very sturdy troop that gains armor with it’s spell, it’ll be extra durable with Divinia giving it Life and also faster to cast when Mistralus enchants it with her trait.
Well, this is just a suggestion, I didn’t managed to get Mistralus to test this theorical team, but at least I believe it’s a team you can assemble without too much trouble except maybe for Divinia that will depend of Event keys maybe. But still you have a chance to get her.