Here is the full list of all 50 Citadel: Forged with Fire achievements.
Tame a Demon
Start or Join a House
Build 50 stone walls, floors, and roofs
Tame an Infernal Dragon
Place your first crafting bench
Place your First Throne
Unlock all structure packs
Discover 4 Towers
Achieve Level 30
Achieve Level 40
Achieve Level 50
Achieve Level 60
Achieve Level 20
Achieve Level 10
Build 100 Ornate or Marble Walls, Floors, and Roofs
Build 50 Wood wall, floors, or roofs
Craft 10 Clothing Items
Craft 500 Gold Ingots
Craft 1000 Health Potions
Craft 1000 Iron Ingots
Craft 1000 Mana Potions
Craft 10 Weapons
Kill 20 Bears
Kill 20 Boars
Kill 30 Death Weavers
Kill 666 Demons
Kill 20 Dragons
Kill 20 Eagles
Kill 50 Imps
Kill 100 Infernal Dragons
Kill 30 Orcs
Kill 10 Sprites
Kill 20 Trolls
Kill 50 Undead
Kill 100 Unicorns
Kill 20 Wolves
Mount a Phoenix
Mount a Unicorn
Fly for 4 hours (gameplay time)
Harvest 250 Precious Stones
Harvest 1000 Mana Rune
Harvest 1000 Stone
Harvest 1000 Wood
Pick Up 250 Items
Discover 20 loot chests
Tame a Large Dragon
Craft 50 Clothing Items
Craft 50 Weapons
Pick Up 1000 Items
Pick Up 10,000 Items