Thran Tome

The Thran Tome was a powerful, ancient book of Thran civilization containing all their knowledge and designs. Urza used it as a construction manual for many artifacts that he created, including the Weatherlight.

During the Phyrexian Invasion, Karn discovered that it held infinitely more information, and because he was strongly linked to the Legacy he soon digested all of its knowledge. Even Urza didn't know the Thran Tome as intimately as Karn came to know it. The Thran Tome was also the main factor in reshaping the Weatherlight to its final form.

At the end of Phyrexian Invasion, The Legacy merged with Karn. All of its powerful parts, including the Thran Tome, united and gave Karn knowledge and power beyond other planeswalkers.