Oh, this is a really nice idea for a black cube! However, I feel it's still distracting that the black mana is Phyrexianized in Wendigo's scavenge cost. It's also somewhat jarring that this is the only creature in the cycle and the only one that does something from the graveyard. How about making it a Nature's Spiral with some upside? E.g. "Return target permanent card from your graveyard to your hand. If it has mana value 3 or less, return it to the battlefield instead."?Infernal Grasp and Night's Whisper already had the pay 2 life on them.
Wendigo is based off of Toxic Abomination, but it needed a bit of a push. pB on Scavenge due to it being more green to add counters.
Eclipse Blade is an effort to find and effect for WB costed at 1pWB that makes sense when cast for both 1B and 1WB.
G and W are open to suggestions. I'd also love to do 2-3 more Phy cards of each Bx combo. I like giving my players small decisions to make. It makes the game more skill intensive without making it drastically more complicated.
EDIT EDIT: Plunderer's Cost should be renamed. There isn't necessarily a cost, unlike Ambition's Cost, which I borrowed from.
Also, I think the red and white one are too similare. Since being a sorcery is considerably weaker, why not make it "Exile target creature, enchantment, or planeswalker"? A little more flexibility and an exile clause seem a nice tradeoff for the slower speed.
Gosh Plunderer's Cost is such a sweet design!