Seekers of the Beyond

When Seekers of the Beyond enters the battlefield, you may exile the top X cards of
target player's library. You may play those cards
for as long as they remain exiled.
{t}, Discard a card: Add {2} to your mana pool.
Spend this mana only to cast spells from exile.
"Only fools believe they have nothing more to learn."
- Gias, Lightseeker