Extraordinary Actions provide new opportunities for extraordinary moments of heroism when the situation is most dire.
A rogue is damaged by the first blow of a Kraken's tentacle attack and uses an Extraordinary Action to escape from its other strikes. A fighter uses an Extraordinary Action to ensure the killing blow on a skull lord. A fatigued wizard uses an Extraordinary Action to give them the vitality to stay in the fight.
Extraordinary Actions let players use hit dice at the cost of exhaustion in order to expand the set of actions a character can do in a given turn or round.
This is an early excerpt of our upcoming work, Xem's Guide to the Underdark. The focus of this module is to immerse the party in a gritty, deadly version of the Underdark where navigation is always challenging and the threat of darkness is always on the mind. This book will be a full setting with cities, npcs, magic items, monsters, and environs all its own.
- from the publisher's blurb