Here is the full list of all 18 Reverse Crawl achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Collect all three of Greybeard's books in one campaign
Unlocked the Horned Demon power
The hardest choice to make
Recruit Greybeard the Exiled Mage
Achieve either of the good endings
Complete two Hero Party quests in one campaign
Unlock the Iron Golem power
The cruellest choice to make
Complete two Merchant quests in one campaign
Achieve the evil ending
Complete two Sage quests in one campaign
Unlock the Red Dragon power
The easiest choice to make
Recruit Violet the Dark Elf
Complete Chapter 7
Defeat a hero
Recruit Bonehead the Goblin Shaman
Trigger an Evil Power