it doesnt have to be just air, tho it can easily be done, as for the other possibilities, i was thinking something like the fire bombs we used against japan in WW2 (which cause A LOT more damage and life loss than the a-bomb, its just not as widely known) tho in permanent form (yes, i love permanents that have activatable abilities)
CARD
name: fire bombardier
play cost: 6
effect cost: each turn, 1
is consumed
effect name: consume (name pending)
one random creature on opponents field is burned
EFFECT
effect name: burn
effect: 1 damage is dealt per turn
-its pretty much the fire poison