Ancestral Vision no mana cost how to play magic gathering

[Swamp]

How come ancestral vision has no mana cost? Can I play it for free?

[Arix]

You can't cast it normally. Nonexistant mana costs can't be paid, and since you can't pay the cost, you can't cast it.

How do you play it then? Find a way around the nonexistant mana cost. If you can play it without paying the mana cost, or by paying an alternative cost, then you can play it that way. The most obvious method is written on the card itself - suspend.