For his -2, he generates a red mana for each Mountain you control
In the early game, you can apply pressure by attacking with multiple creatures and tokens and keep them protected from your opponents spells
It is entirely the ability to pay four life to draw a card that pushes Library into the realms of great cards
Arcades, the Strategist and Felothar the Steadfast are the two most popular, but you can also look to Doran, the Siege Tower, Doran, Besieged by Time, and Plagon, Lord of the Beach as some secondary choices
You draw X cards and the chosen creatures get +X/+X and gain trample until end of turn, where X is the difference between the chosen creatures' powers
I assume this is in preparation for Assassin's Creed, but it's still pretty weird