No, regardless of power, a creature with defender cannot attack
This two-mana staple slots perfectly into the equipment-heavy Limit Break deck, tutoring out gear with ease, and the market has noticed, its jumped from under $20 to around $50 in recent listings
None are creatures and provide more immediate and impactful effects
The card has generated lots of chatter, more I think because of its adorableness than function
Top-decking this is bad, but if you can put a creature into play for free, its not tempo loss (Fires of Invention was strong for this reason)
The set had a gothic horror theme that played into dark transformation, so you would play the card as side A and the transform it into side B, Mark Rosewater, Magics head designer, told io9 in a statement over email