Yup, I have to say it's saved me so many times, it hasn't learned Giga Drain yet but Leech Seed, Sleep Powder & Cotton Spore works wonders, especially on Gym battles so thanks!
If I may suggest a Pokemon for a Crystal Flying Monotype it would have to be Jumpluff. It destroyed in mine with Sleep Powder, Leech Seed, Synthesis and Giga Drain. Seriously it dominated.