I have prepared this chart for the RAID players to see what are the chances of getting Rare Skill Tomes (books), Epic Skill Tomes (books) and Legendary Skill Tomes (books).
Currently there is no way to "farm" skill tomes in the game - they come only from shop purchases, tournament/event rewards and the Clan Boss chests. The chances below relate to the Clan Boss.
The "Holy Grail" for RAID players is to consistently / daily achieve the Transcendent Chest in the Ultra-Nightmare Clan Boss, but it is already also excellent to achieve the Ultimate Chest in the Nightmare Clan Boss.
You will notice also that as you progress in RAID you unfortunately stop getting Rare Skill Tomes from the Clan Boss.
Thanks to Bobo for the data.
