You will earn this trophy naturally by working your way through the challenges as Challenge 7, (Nissa), requires you to do 26 damage to her in a single turn of combat anyway.
Start by casting Terror on her Elvish Champion to destroy it, then declare attacks with everything. You should be prompted to use Flameblast Dragon's ability - use it on your Sprouting Thrinax and destroy it, giving you 3 tokens.
She'll block one of your creatures but you'll still have enough damage on the board to win and claim your trophy.