If you have extra mana, why not get two copies instead of one
A powerful card that works in the deck but not for the deck if that makes sense
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of this ability)
This deck packs a variety of ramp spells like Rampant Growth, Arbor Elf, and Overgrowth to let you accelerate into Gargos and get ahead of your opponents
Meanwhile, you have a built-in engine to invest extra mana from your Swamp-tapping ways with extort, and its a clock as well
Secret Lair drops are usually very small in terms of the number of cards they comprise