Self-Replicating Spell Transcription -- this spell will always appear to be just barely one level higher than the mage would normally be able to understand. Should the mage transcribe the spell into his own spellbook for later study, the SRPT will immediately copy itself multiple times in the book until all pages are filled with it, even to the extent of wiping out other spells to make use of the page space. Variations on this spell include a time-delay or trigger feature (copies don't occur until after X hours pass), and an infectious feature (copies to other spell books and scrolls in contact).
Helpful Spell Suggester -- this spell appears innocuous at first, seemingly a 0-level cantrip of no particular use. However, the HSS is actually attached to another written spell (on the previous page of the spell book), and when that more-useful spell is transcribed to a mage's own collection the HSS copies itself as well. Thereafter, whenever the mage casts a spell from that spellbooks or scroll, the HSS will activate, causing the illusion of other spell pages to pop into the air in front of the mage's face as helpful suggestions -- "Try THIS spell next!"