Mercurial Geists

Creature — Spirit

Produces: nothing.

Cares about: an instant or sorcery being cast.

Partners

140 cards can cause an instant or sorcery being cast.

1. Mission Briefing — When Mission Briefing is cast, Mercurial Geists gives +3/+0
2. Sorcerous Squall — When Sorcerous Squall is cast, Mercurial Geists gives +3/+0
3. Kylox, Visionary Inventor — When an instant is cast thanks to Kylox, Visionary Inventor, Mercurial Geists gives +3/+0
4. Chandra, Acolyte of Flame — When an instant is cast thanks to Chandra, Acolyte of Flame, Mercurial Geists gives +3/+0
5. Chandra, Flame's Catalyst — When an instant is cast thanks to Chandra, Flame's Catalyst, Mercurial Geists gives +3/+0
6. Chandra Ablaze — When an instant is cast thanks to Chandra Ablaze, Mercurial Geists gives +3/+0
7. Jace, Vryn's Prodigy // Jace, Telepath Unbound — When an instant is cast thanks to Jace, Vryn's Prodigy // Jace, Telepath Unbound, Mercurial Geists gives +3/+0
8. Sword of Once and Future — When an instant is cast thanks to Sword of Once and Future, Mercurial Geists gives +3/+0

61 other cards cause it too, equally specific. The ones shown are the best connected.