Here is the full list of all 64 Relapse achievements.
The base game contains 57 achievements, and there is 1 DLC pack containing 7 achievements.
Tutorial completed
Defeated Titan
Defeated Leshy
Defeated Cyclops
Defeated Reaper
Defeated Lich
Defeated Mech
Defeated Dragonkin
Defeated Dragon
Defeated Slayer
Defeated Blue Spirit
Defeated Red Spirit
Defeated all act 1 bosses
Defeated all act 2 bosses
Defeated all act 3 bosses
Defeated Treant
Defeated Earth Demon
Defeated Fungi Bandit
Defeated Fungi Mage
Defeated Bandit
Defeated Werewolf
Defeated Necromancer
Defeated Jakki Mage
Defeated Jakki Bandit
Defeated Obsidian Golem
Defeated Elemental
Defeated Undead Warrior
Defeated Blue Guardian
Defeated Green Guardian
Defeated Red Guardian
Defeated Blue Drake
Defeated all act 1 elites
Defeated all act 2 elites
Defeated all act 3 elites
Beat Act 1
Beat Act 2
Beat Act 3
Defeated Hobgoblin
Defeated Bone Golem
Defeated Spider Queen
Defeated Slime King
Defeated Elite Guard
Defeated Warlock
Defeated Rune Keeper
Defeated Ogre Shaman
Defeated Ogre Warrior
Defeated Ogre Bandit
Reached max level with Berserker
Reached max level with Ritualist
Reached max level with Elementalist
Reached max level with Beast Master
Reached max level with Crusader
Knows a good deal when they see one
Upgraded every talent to max level
Defeated Djinn
Defeated Forsaken
Defeated Ifrit
Beat Ascension 1
Beat Ascension 2
Beat Ascension 3
Beat Ascension 4
Beat Ascension 5
Beat Ascension 6
Beat Ascension 7