Mulligans
The idea here is you play Alex then the next turn you play Vargoth + Thalnos + double mind blast. This is an 18 damage combo. Varagoth + double mind blast is 15, just like how people have suggested holy fire+ double mind blast, however the most you can get on one turn is 15.
The advantage to Vargoth is the flexibility. You can also use Vargoth to double up on board clears as well as divine hymn in a pinch.