Sakuya: Effectively teleport with time-stop. Sanae: Use miracle evocation to slant fate to her advantage. Youmu: ? (She'd better not have brought Yuyuko...) Yukari: Teleport with planar rifts. Reimu: Fervor fueled by sheer desire and desperation.
Other possible entrants:
Marisa: Well-tempered expertise at thievery. Reisen: Hypnotize everyone into staying away from what she wants. Eirin: Flood the store with a soporific mist that affects everyone but her and the shopkeeper. Tenshi: Create repelling tremors around herself. Flandre: Break the eyes of some floor tiles to create blocking holes. Patchouli: Have familiars do all the work for her. Wriggle: Send ants in to be unobstructable cargo convoys. Best results with fire ants. Nue: Disguise herself as unassuming fixtures.
As long as they don't trample any plants and thus incur Yuuka's displeasure, it should at least stay interesting.