Having a sacrifice outlet in your command zone is powerful enough, but getting death triggers and getting to double up on them can be strong as heck
Unfortunately it comes into play tapped, probably negating the biggest upside Reflecting Pool has
Rather than pay mana, you can pitch any blue card from hand to counter a spell for free
Then exile it.) "Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack." To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions
I chose mono-black Zombies because WotC has provided a ton of support for the Zombie creature type over the decades, including lots of reprints, so its pretty easy to pull together a solid deck without breaking the bank