The GL one isn't a mini. It's just from the regular GL ongoing that had issues going during BN. I think you already have it in your cart. It's this one: https://www.comixolo...kTGlzdC8yMzgyMQ
And it is essential.
Blackest Night Batman is fun because it's basically an Elseworld where all of Gotham has to hold off a Zombie Invasion. You get to see characters doing things that you'd have never thought about before. Red Robin with a flamethrower is super badass, too.