There are three different books going on here. Allow me to explain!
Spellbook Vol. 1: A collection of five chapters, written by me and illustrated by the artists listed on the main page. This collection is just about ready to print, so I won't be adding anything new to it that may delay its production.
Spellbook Vol. 1.5: This is a digital-only collection of mini-chapters, about 1/3 the length, written by me (with a guest chapter written by Tristan Tarwater) and not illustrated. We unlock a new mini-chapter for every ten retweets this tweet gets: https://twitter.com/Taylor_CS/status/963617503766130688. These chapters will deliver as completed to all backers at the digital tier and higher. If retweets get high enough, I may bring on more guest writers.
Spellbook Vol. 2: This is the next big step for Spell: The RPG. All chapters will be written and illustrated by other creators and will be full length. The stretch goals of this campaign allow Whimsy Machine to begin production on the chapters much sooner than would be otherwise possible. Digital versions will be delivered to all backers of the digital tier and up as they're completed—much later than other digital deliveries—and the plan is to collect it in print once all the chapters are done.