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.
Complete two Merchant quests in one campaign
Complete two Hero Party quests in one campaign
Collect all three of Greybeard's books in one campaign
Complete two Sage quests in one campaign
Achieve either of the good endings
The hardest choice to make
The easiest choice to make
Complete Chapter 7
Trigger an Evil Power
Recruit Greybeard the Exiled Mage
Recruit Violet the Dark Elf
Unlock the Red Dragon power
Recruit Bonehead the Goblin Shaman
Unlocked the Horned Demon power
Unlock the Iron Golem power
The cruellest choice to make
Achieve the evil ending
Defeat a hero