Underground Sea is never going to cost you two life, while Watery Grave will some percent of the time
Granted, it's at sorcery speed instead of being able to do it on someone else's turn to start off a Storm combo with a bit of a boost, but in all likelihood it's still going to do more for you in a mono-black build than a simple Dark RitualDark Ritual will, for the same mana cost
On top of that, it also has two additional modes, letting you snipe your opponents graveyards while generating advantage
Rakdos Adventures: An aggro deck with a lot of reach and the potential to grind, but the manabase leaves a little to be desired
Zekrom's design is inspired by dragon and electric motifs, featuring a sleek, aerodynamic body with robust, powerful wings and a generator-like tail that harnesses electricity
It hits for 80 with 1 energy and energy gain, and the extra damage in return shouldnt be that much of a problem since your opponent probably wont overpower you at this stage of the game