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

Sunfrill Imitator copies exactly what was printed on the original creature, with the listed exceptions (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or any Auras or Equipment attached to it, or any non-copy effects that have changed its types, color, power and toughness, and so on.

If the copied creature is copying something else, then Sunfrill Imitator becomes a copy of whatever that creature is copying.

If Sunfrill Imitator copies a legendary creature, Sunfrill Imitator will also be legendary, but because its name remains Sunfrill Imitator, the "legend rule" won't cause either of them to be put into the graveyard.

If the copied creature is a token, Sunfrill Imitator copies the original characteristics of that token as stated by the effect that created the token. Copying a token doesn't make Sunfrill Imitator a token. Similarly, if Sunfrill Imitator itself is a token, copying a nontoken permanent doesn't make it stop being a token.