The spat between the Greens and NZ First has escalated, with Green MP Barry Coates suggesting (on The Daily Blog) that the Greens could deny confidence to a Labour - NZ First coalition and force another election if Winston locks them out of government.
Its an empty threat, in that if Labour needs Winston as well as the Greens, he can almost certainly switch his support to National (and in the event of a confidence loss, he would have space to do this, because the Prime Minister needs the confidence of the House to call an election). And that alone means it is a stupid one. But it does demonstrate just how angry the Greens are getting at the prospect of being taken for granted by Labour again.
As for what they should do about it if Labour doesn't significantly lift its performance and a three-way deal is necessary: choose no deal over a bad one. Sure, give Labour - NZ First confidence and supply, but unless they are offering serious policy concessions on areas of core Green interest, and policy vetoes over NZ First racism, give them nothing else. Then use their effective legislative veto to extract concessions piecemeal, and bargain hard over anything not in the Green manifesto. Don't even give them a house management vote (as the Maori Party has done for National) - if they want urgency, then they can demonstrate the need. And if they want policy which isn't already backed by the Greens (and isn't contrary to their values), then they can fucking pay for it.
Labour and NZ First can either have the Greens inside the tent pissing out, or outside the tent setting it on fire. The choice is up to them.