The ShiftstonedEternal Power Calculator is a deck-building tool that visualizes your odds of drawing enough Influence and Power based specifically on the cards found in your deck.
Can someone explain why Mandevilla is in every deck -- it looks like an expensive, slow kill spell that, if used on a small unit, will give you a tiny lifesteal unit, and if used on a real threat gives you nothing. Devouring shadow at 3 seems more appealing (counters recursive nonsense) or deathstrike at 4 is more versatile. Everyone's running it, though, so what am I missing -- mandrake synergy?
I've been playing with a similar deck, and Mandevilla never feels bad. Use him to clobber an annoying token, you still have a lifesteal dude left. It can be a 5 mana remove-anything spell. Worst case, slap him on an empty board, you have a 5/5 with lifesteal for good D'Angolo Might fuel.
The ability to run it out as a 5/5 to stabilize against aggro or draw cards off of Might is great. Killing a small unit and being left with a 2/2 or 3/4 Lifesteal is fantastic. Being a slow expensive Deathstrike is a fine alternate mode to gain access to those modes - Deathstrike is not even close to more versatile than a unit that has Deathstrike as one of its three modes. The power in expedition is atrocious so you can't support Devouring Shadow in a deck with double pips in the non-shadow faction. You can fetch Mandevilla with Sinister Rumors or Grenahen (and rumors on a 0/0 Mandevilla is still a Deathstrike).In this particular deck it also gets buffed by Ageless Mentor and Vine Grafter.