Just picked up the game and was playtesting combat with a few friends. Put them up against a werewolf with Bite (M): Reach 1 and Two Claws (M) : Reach 2.
Both players were using broadswords ( Reach 2). Assuming the enemy has guard, there is no change in attack rolls against Two Claws.
If it is a part of the enemy’s body, is it just assumed that they always use the longer reach?
You choose which (natural) weapon the NPC uses to attack.
If the attack is with the Bite, Reach 1 applies.
If the attack is with the Claws, Reach 2 applies.
If you choose to attack twice, by making the Swift Attack Momentum spend, which you could get for only 1 Momentum/Doom instead of the usual 2, because Bite and Claw are different weapons, then, still, the Bite attack has Reach 1, so +1 Difficulty versus Reach 2 weapons, the Claws have Reach 2, so no raise in Difficulty versus Reach 2 wepons.
Some creatures have more than one or two natural weapon attacks. You simple choose the one they are using their Standard Action to attack with. That weapon determines the Reach for that specific attack.
I was just about to answer this, but I can see that @FrankF is answering… do what ever he says.