Okay, templating again, as this causes rules issues. "Creature spells named "Princess Luna" cannot be cast. If a creature named "Princess Luna" would enter the battlefield, it doesn't instead." She could probably cost one or two less. Her activated ability might require her to tap though.
Less narrow than Celestia. I probably wouldn't want to cast her for 8 mana unless the set supports excessive ramping, but she'd be a prime target for a reanimation spell (possibly broken in that specific context, but so are numerous official cards like Iona [link]).
There are some cards I threw in to add more mana, but the fact that she's flying and shadow and can destroy creaturesfor two mana...I dunno I'd have to remake the card almost completely to lower the cost.
Oh, I think she's fine; Timmies will probably love her. I'm a Spike, so don't mind me... (I'd play a weaker and cheaper version, but catering to different demographics is important. In fact, I should probably include some "awesome, who cares if it costs 10 mana" cards in my set, as well as some "weird, comboriffic and a little overcosted" ones for the "I play this because others don't" Johnnies.)
"Creature spells named "Princess Luna" cannot be cast. If a creature named "Princess Luna" would enter the battlefield, it doesn't instead."
She could probably cost one or two less. Her activated ability might require her to tap though.