Probably the most interesting class from a mechanical standpoint is the wizard. The wizard card has the following stats:
Trait 1: The wizard may pay a spell's cost in spellbook pages to return the spell to his hand once cast instead of exiling or discarding it.
Trait 2: A wizard may sacrifice four spellbook pages to draw a card.
Now, this doesn't really mean a lot unless you look at the wizard's spells. Most of the damaging spells, except the weakest ones, have the text that they are exiled once cast. For example, fireball:
Effect: Deals 6 damage to all enemies currently on the field. Exile after casting.
This means that if we had 5 spellbook pages on hand, we could return this card to our hand instead of exiling it. This means, not only can we cast it again, but we could also discard it for mana (keeping it in the graveyard so its available after a reshuffle) or even cast it again normally, exiling it then.
The grand scheme of this mechanic is to make wizards powerful, but only if they plan their moves correctly. Using a fireball early might win an encounter, but you may miss that fireball later, when it was exiled and you need it again. As the encounters wear on, and the wizard casts more and more spells, eventually he will run low on good spells unless he is taking careful account and spending spellbook pages wisely. Most of the wizard's best cards revolve around this mechanic, like time stop. Time Stop allows the wizard to cast extra spells, so if he had a lot of mana and a hefty investment in spellbook pages, he could cast the same spell over and over again in one turn.
Wizards have some support items too. Scroll, for example, is like a free copy of one of your spells. When you equip a scroll, you select a spell in your hand. You can discard scroll and cast that spell for its cost in spellbook pages. This would be very useful for any spell that would be exiled, as you not only get to keep it in your hand, but you pay its cost in spellbook pages rather than mana.
Another useful spell is Master's Arcanum. This is a 4 cost effect with a 1 persist cost. You gain one spellbook page per turn, and can pay 2 mana to gain 2 spellbook pages once per turn.
Finally, there is a treasure called the Ring of Wizardry. This treasure costs 3 to equip, but once equipped you can place a counter on this ring for every turn that passes. Once three counters are on the ring, you can remove all counters and unequip the ring to restore one exiled spell that has been played this game to your hand.