Spin-down, I think that's the effect where you "Stun" the opponent after hitting them so much, that they begin to "spin" a downward spiral away from you. Kind of like how Hisou & SWR did when getting that 100%. It grants them temporary invincibility. 9J has Tenshi (I think she's the opponent there) at the highest difficulty, she she'll try to dodge a lot. I've been using Reisen B for most of my Sky Adventure, and a good combination of EX skills, Melee, Charge Spell Cards, will assure you a spin-down (just need to know the correct pattern to not allow the enemy some breathing room)