The fewer colors in your deck, the better this card ends up being because you wont have to pay as much life
We rarely see Gengar with the complementary red background this card boasts, and matching the color in its eyes is an excellent bonus that makes this card stand out
The ability to turn off life gain is important for decks that can deal a finite amount of damage, and, unlike Stigma Lasher, we can control who we hit with its ability, which functions outside of combat
Being able to (potentially) cheat out cards like Worldspine Wurm, Shriekwood Devourer and Thunderfoot Baloth is nice, but there are some solid reprints, too
Mystic Snake is a lot worse of a Counterspell than Plasm Capture as a mana injection tends to be more use than a 2/2
Barrowgoyf's power is equal to the number of card types among cards in all graveyards and its toughness is equal to that number plus 1