we're not actually in mono green. we're just keeping our options open. although by that pick we will have 10 playable cards in mono-green. but the cost of adding a second color is so minimal that it's almost certainly worth it. we have bite so I guess we're leaning black already, although I'm ready to jump ship if we open a red bomb or something. so the question is, is Ambush roughly as good as Unmake?
Unmake is a divination for two strong creatures. Unmake for Silverback and Siege Wurm is basically GG. Unmake can pull us back from losing, whereas I think Ambush is only good if we're already at least at parity. I'm gonna say that Unmake is better enough to run the risk that we don't wind up playing it.
I don't see it this way. We keep saying that Ambush is dependent on other cards (it is) but how isn't Unmake? There is no lock that we will have two strong cards worth pulling from our graveyard. They are both dependent on other cards, so that point seems moot to me.
If we are losing, do we really want to spend 5 mana (or tap some creatures, leaving us more vulnerable) to cast a spell next turn? By then, it seems like it will probably be too late.
Our deck looks like it may be pretty slow. If so, Ambush helps us bridge the gap to our bombs against faster decks. Unmake helps us to break ties against decks with similar speed.
I'd rather worry about getting to the point of playing our hornet queen than worry about getting it back next turn.