If the countered spell had in its mana cost, include the value chosen for that X when determining how much mana to produce. For example, if you counter a spell that costs with X equal to 5, you'll produce six mana.
2013-04-15
Your precombat main phase is the main phase that happens immediately after your draw step, not any other main phase.
Counter target spell. At the beginning of your next first main phase, add X mana in any combination of colors, where X is that spell's mana value.