There are 4 types of pages: Tumidum, Audere, Gratanter, Congeriae I have 15 pages but only 1T 7A 7G and 0C this cant be random so how this work? What should i do to get Congeriae page?
You get a Tumidum page by completing 4 helltower achievements. The other three are completely random, and are obtained by gifts on helltower.
Congeriae was recently introduced a couple days ago, which may contribute to the fact that you don't have any of them yet.
If you wish to farm spellbook pages, log in and play a game once an hour. You'll find that there is a gift spawn within 30 seconds of joining a server.
there are actually five page types. the fifth is in the games files but it isn't dropping yet. it is called veteris these pages have meaning
Pages of Gratanter - Swollen or distended; confidence Pages of Audere - Having courage; being prepared Pages of Congeriae - Chaos; collection or accumulation Pages of Tumidum* - With joy or rejoicing Pages of Veteris* - Long standing; ancient or experienced
tumidum is joy and rejoicing which would explain the unlocking via achievement.
congeriae is collection or accumulation so it might have something to do with the amount of pages you already collected
and 1 veteris page was unlocked after collecting 27 other pages.
as for the other two I believe they are just starter pages. pages you accumulate until you get the manntastic four achievement and until you've gathered enough pages to start collecting congeriae.