When a permanent is copied, the only thing that's copied is what's actually printed on the card and other copy effects. (With a few small exceptions** not relevant here–see the footnote for more.) As such, when
Clever Impersonator copies
Hypnotic Siren, it doesn't copy the bestow effect. All it sees is the card itself.
This means that
Clever Impersonator will enter the battlefield as a 1/1 blue Siren Enchantment Creature with flying. It will not be an Aura.
**Copy effects also take into account face-down status (copying a morph effectively gives you a permanent morph), plus a few rare ETB choices that set power and toughness. (Copying Primal Clay gets you the same choice as was made for the original Clay.) These are generally glossed over because they're rarely encountered (morph in Standard notwithstanding) or relevant.
Edited Callum Milne (Oct. 9, 2014 06:58:46 PM)