If the copied creature is a token, Naga Fleshcrafter (or in the case of its renew ability, each other creature you control) copies the original characteristics of that token as stated by the effect that created that token.

You can choose not to have Naga Fleshcrafter enter as a copy of another creature. If you do, it will just be a 0/0 Snake Shapeshifter, and unless another effect is increasing its toughness, it will be put into your graveyard.

If the copied creature has in its mana cost, X is 0.

Both of Naga Fleshcrafter’s abilities copy exactly what was printed on the original creature and nothing else (unless that creature is copying something else or is a token; 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, or any non-copy effects that have changed its power, toughness, types, color, and so on.

If a card with a renew ability is put into your graveyard during your turn, you can activate that ability if it’s legal to do so before any other player can take any actions.

If the copied creature is copying something else, then Naga Fleshcrafter enters as whatever that creature copied. Similarly, its renew ability will cause each other creature you control to become a copy of whatever that creature copied.

Any “enters” abilities of the copied creature will trigger when Naga Fleshcrafter enters. Any “as this creature enters” or “this creature enters with” abilities of the copied creature will also work. Activating its renew ability doesn’t cause any creatures to enter the battlefield, and as such, these kinds of abilities won’t work with Naga Fleshcrafter’s renew ability.