Shadows of Abaddon is inspired by the Soul of Two Realms storyline and adds a significant amount of "lore dumps" and mechanical depth. tModLoader - Shadows of Abaddon mod
You can access the mod through several official channels depending on your version of Terraria: shadows of abaddon download
Standard versions can be found by searching "Shadows of Abaddon" directly within the tModLoader in-game browser. Shadows of Abaddon is inspired by the Soul