Just finished reading the 9.6/10 review and build guide for Clair Obscur: Expedition 33 here on Game Vault, and wanted to share the Lumina combination that carried my party through Expert difficulty in Act 2:
1. Master "Energising Parry" (+1 AP on every successful Parry) and "Counterattack Mastery" (+50% Counter damage) across all three active party members.
2. Have Lune open Turn 1 with Wildfire to apply Burn to all enemies and generate Light/Fire stains.
3. Have Maelle immediately cast "Swift Stride" on the burning boss—which transitions her straight into Virtuose Stance (+200% damage!) on Turn 1 without needing defensive setup turns.