Here is the full list of all 37 TOME: Immortal Arena achievements.
Achieve Harbinger Level 20
Unlock 3 Relics for a Guardian
Unlock 6 Blessings
Complete the Beginner Tutorial
Win 20 PvP Matches
Unlock a Relic for a Guardian
Win your first Coop Vs AI Match
Win a match as a Slayer
Unlock 20 Guardians
Win a match as a Pusher
Win a match as a Tactician
Win 5 PvP Matches
Unlock a Blessing
Win a match as a Tank
Win your first PvP Match
Unlock 5 Guardians
Unlock 1 Guardian
Unlock a Dance for a Guardian
Achieve Harbinger Level 5
Win 5 Coop Vs AI Matches
Win 50 Coop Vs AI Matches
Win a 1v3 Practice Match
Win 100 PvP Matches
Win 1000 PvP Matches
Unlock 18 Blessings
Achieve Level 6 in all Domains
Achieve Level 6 in the Fire Domain
Achieve Level 6 in the Air Domain
Achieve Level 6 in the Water Domain
Achieve Level 6 in the Earth Domain
Achieve Level 6 in the Death Domain
Achieve Level 6 in the Creation Domain
Unlock 30 Relics
Unlock an Ascended Skin for a Guardian
Unlock 20 Ascended Skins
Achieve Harbinger Level 50
Achieve Harbinger Level 100