Militia Y intends to burn massive amounts of wood in order to produce carbon monoxide to be used as an air contaminant in warfare.
Defence: to be asked as a follow-up question.
Time period: ancient (140 AD thereabout).
Plan: Arrive at battle site long before enemy arrives,
Settle massive load of wood in strategic places.
The rest lies in the bows of the archers (with flaming arrows of course).
Transport: Carried by massive griffins (on platforms tethered with steel chains).
Although! Militia Y would prefer to test a recent theory that wet wood produces more carbon monoxide
No worries, carbon monoxide also poses a health hazard in ventilated areas, thus, there might be feasibility of open air carbon monoxide poisoning.
However, realistically, is this strategy a little too fantastical, even for a fantasy world?