History Teacher — Sagas you control have
read aheadRead ahead is a keyword found on some Saga cards. “Read ahead” means “Chapter abilities of this Saga can’t trigger the turn it entered the battlefield unless it has exactly the number of lore counters on it specified in the chapter symbol of that ability.” See rule 714, “Saga Cards.”
Each Saga with read ahead has the intrinsic abilities “As this Saga enters, choose a number between one and this Saga’s final chapter number” and “This Saga enters with the chosen number of lore counters on it.” See rule 714.3b.
Multiple instances of read ahead on the same object are redundant. (CR 702.155). (As a Saga enters, choose a chapter and start with that many lore
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1). Skipped chapters don't trigger.)
Doctor's companionA Doctor commander may have a creature with this ability as a second commander when the deck-building condition is met. (CR 702.124) (You can have two commanders if the other is the Doctor.)