score:4
There are four terminological divisions of nirvana, and none of them is mara.
Non-duality does not mean “that opposing terms depend upon each other”. Rather, we posit three types of dualistic appearances :
A consciousness that is free from the three is said to be “free from dualistic appearances”. By extension, the person who is the object-possessor knowing “in a non-dualistic manner” is also said to be free from dualistic appearances.
Here is an example: Conventional truths do not appear in the perspective of the wisdom directly realizing emptiness. True existence does not appear to the superior's exalted wisdom directly realizing emptiness. There is no appearance of the object and the consciousness as being to different substantial entities to that consciousness. Because the wisdom directly realizing emptiness is free from the three types of dualistic appearances, we say that he who directly realizes emptiness does so “in a non-dualistic manner”. He is free from dualistic appearances (as long as he abides in meditative equipoise on emptiness).
You are right to oppose mara to skillful means. Maitreya/Asanga's Ornament of Clear Realization, says: “The first application in skillful means is called application in skilful means which is victorious over the four mara-demons”.
However, there are four maras:
Non-abiding nirvana is freedom from the four (and is the final true cessation), therefore it is not mara.