You may cast that card without paying its mana cost if the spell's mana value is less than the number of Mountains you control
To start your day, some good options include Skemfars Bounty (pg 108), Jumpstart Energy Bowls (pg 184), and Jade Toast (pg 210)
I had been playing for a few years before then, but Mirrodin felt like the set where I really started to come into my own as a player
Product Details At the beginning of your upkeep, if an opponent controls more lands than you, you may search your library for up to three basic land cards, reveal them, and put them into your hand
The latter scenario, known as decking out, transpires when a player is unable to draw a card when required, adding an additional layer of strategic depth to the game.