Vengevine is a unique card because to return from the graveyard, it actually requires two creatures to be cast in the same turn, which means traditional Dredge cards like Bloodghast and Narcomoeba (which enter the battlefield but are not cast) have no value when it comes to returning Vengevine from the graveyard to the battlefield
Id want to include Helium Squirter, Elusive Krasis, and Skatewing Spy to make combat easy
The second will come when trading, when something looks a bit off you should immediately start to focus more and look for other issues
If they have eight or more cards in their graveyards, your Soaring Thought-Thief, Into the Story, or Lullmage's Domination go from good to great
To me, thats enough to make this worth considering and maybe even quite good