March from Velis Vel

"Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."

A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.

If the copied creature is copying something else, then the lands become copies of whatever that creature copied.

The lands copy exactly what was printed on the original creature and nothing else (unless that permanent is copying something else; see below). They don't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, and so on.

You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.

You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.