The Maori Party and the Greens are discussing an informal alliance ahead of the election. This makes a lot of sense. The two parties vote together on most issues (more than they vote with any other parties) and have fundamental principles in common.
Either major party will probably need the support of one or both of them to govern after the election. By undertaking to negotiate with the major parties together, the Greens and the Maori Party will present a solid bloc that will ensure their policies are taken into account no matter which major party governs.
The Greens and Maori Party have so much in common because they represent strands of left-wing ideology and although they both differ strongly with Labour on a number of important issues they share fundamental ideals . It is not realistic to think they could work with National, no matter how much John Key practices his hongi. The Maori Party and the Greens have very little common ground with National and both parties would face internal collapse if they did a deal with the Right. So, a Green/Maori Party alliance is likely to end up supporting Labour in government. In doing so, it would serve as a valuable counter-weight to Labour’s tendency to be timid and take half-measures.