Thats probably mainly due to the fact that it also exists in Revised
If you've had one Human enter the battlefield this turn (including Eowyn herself, on the turn you play her) will reward you with two more Human Knights with Trample and Haste
Glass Casket made perfect sense as an artifact, but it felt wrong to us that True Love's Kiss could save Sleeping Beauty, but not Snow White, so we changed this card from just destroying enchantments to destroying artifacts or enchantments
Some competitive deck builds run with as few as 4 energy cards, but theme decks can have as many as 20 or 30
Mostly, this gives you a Zombie at the end of your turn if you lost 2 or more life, and losing life on your own turn isnt something that will just happen -- youll have to create situations to make that part work, and even though Black is always capable of doing that in Limited, it is highly unlikely you get a critical mass of those cards going that allows you to consistently make a Zombie, and you probably need to get at least two out of this for it to feel worth it