Some ideas -
Natural Hazards (how the moor can kill you): sinkholes, quicksand/sucking mud, poisonous flora, poison waters, lightning strikes, toxic fog, disease.
Lures (things that get the moor to kill you): will-o-wisps, fey sprites, imps, ghosts, illusions, elemental creatures, swamp mimics.
Protectors (things that keep civilization out of the moors): swamp thing, plant creatures, spirits of the dead, new orc warlord, swamp troll witch, crazy hermit, druid/ranger coven, treants.
Hunters (things that stalk the moors): normal hunter with an environmental twist (e.g. mangrove jaguar, mud bulette, sentient moss slime, etc) or carnivore typical to swampy lands (alligators, piranha, snakes, giant insects).
Trappers (things that set traps in the moors): giant trapdoor spider, giant antlion, mud monster, giant carnivorous plants, hangman tree, humanoid traps (bear traps, pungee stick pits, deadfalls, etc).
You should also consider what kind of factions exist in the moors; the two most obvious choices being a Ranger/Druid group, and of course the orcs that the party are following. I am a fan of runty, seemingly harmless creatures (cowardly swamp goblins) which stalk the party, hanging around and waiting for them to fall - on their own, they don't interfere with the party and flee if attacked, but every once in a while the group comes across some sign that these harmless creatures are actually quite brutal (maybe they watch the swamp goblins skeletonize a dead crocodile within a matter of seconds or something).