In casual mode, players can play any revealed scenario on the world map regardless of achievements or whether it has been completed in campaign mode.
Players can still gain experience and money, loot treasure tiles, complete battle goals, and make progress toward completing their personal quests, but any story text or rewards listed at the end of the scenario are disregarded.
A party in campaign mode can switch to casual mode to go through a scenario they have already completed, but it is strongly recommended that a party not undertake a scenario in casual mode that they haven’t yet experienced in campaign mode.