While it is copying a creature, Cursed Mirror does not have "{T}: Add {R}" (unless the creature it's copying also has that ability).

If something else becomes a copy of Cursed Mirror while Cursed Mirror is a copy of a creature, the duration of the effect is not copied. The new copy will still be a creature (with haste) after Cursed Mirror stops being a copy at the end of the turn.

Any enters-the-battlefield abilities of the copied creature will trigger when Cursed Mirror enters the battlefield. Any "As [this creature] enters the battlefield" or "[This creature] enters the battlefield with" abilities of the copied creature will also work.

Cursed Mirror copies exactly what was printed on the original creature (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 has {X} in its mana cost, X is considered to be 0.

If the copied creature is copying something else, then Cursed Mirror enters the battlefield as a copy of whatever that creature is copying.

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

If Cursed Mirror somehow enters the battlefield at the same time as a creature, it can't become a copy of that creature. You may choose only a creature that's already on the battlefield.