Sweep the Skies

You can choose any value for X. Choosing a higher value for X lets you pay more mana and thus spend more colors of mana to cast it. For example, if you choose 0 for the value of X and pay {U}{U} to cast Sweep the Skies, you'll create one Thopter. If you choose 4 for the value of X and pay {W}{U}{U}{B}{R}{G}, you'll create five Thopters.

If you cast a spell with converge without spending any mana to cast it (perhaps because an effect allowed you to cast it without paying its mana cost), then the number of colors spent to cast it will be zero.

If there are any alternative or additional costs to cast a spell with a converge ability, the colors of mana spent to pay those costs will count.