It isnt the worst, but its bad by todays standards
Some people are calling it "the end of the game as we know it." Indeed, it bears a striking resemblance to something I "predicted" in World War M, the fictional article I wrote in 2012 about what it would take to kill Magic
Mirkwood Bats Marcy: This list isn't meant to exactly point out synergies, but that's just to say that Mirkwood Bats finds a lot of comfortable homes in decks that generate tokens that are then easily used up, such as from Lotho, or any number of food token generators in the LoTR set
Should you not be festive enough, presumably the card will fizzle, however, that ruling isnt set in stone
But why exactly was it banned
While it is a basic energy card, there may be better options like Dark Patch or Darkrai Prism Star for specific dark-type decks