In a recent Curse of Strahd session,
As written, lycanthropes cannot damage one another as they have immunity to non-silvered, non-magic attacks (and see: Can a Werewolf actually hurt another Werewolf?)
In Curse of Strahd, there are two opposing factions of lycanthropes. I will call them Team Black and Team Gray; they are identified in the spoiler block above. Given that they are opposing, it seams reasonable that they sometimes come to blows – except that they cannot harm one another. It may be that they simply avoid one another and try instead to focus on influencing the other beings in Barovia.
However, suppose they did come to blows? If a group of Team Black fought a group of Team Gray, what RAW techniques could they use to harm one another?
1. Arming themselves with torches.
If they know a fight was coming in advance, making sure they went equipped with torches is a likely strategy. A lit torch does 1 hp of fire damage on a melee attack, and lycanthropes are not immune to fire damage.
2. For Team Gray, employing the DMG optional rule for Massive Damage (p.273).
When a creature takes damage from a single source equal to or greater than half its hit point maximum, it must succeed on a DC 15 Constitution saving throw or suffer a random effect determined by a roll on the System Shock table
Team Gray has several different attacks that do up to 10 damage, but with a Critical hit, these can do up to 18 points. A hit doing 15 or more damage would be half the hp maximum of a member of Team Black. Could such a hit require a Massive Damage save and roll? (or would this be prevented from their immunity?) If this was allowed, perhaps one member of their team would try shove attacks, making a member of Team Black prone so that the other members of Team Gray were more likely to get a crit?
Note that this is not an option for Team Black, as none of their attacks, even with a Critical hit, will approach half the hp of Team Gray.
3. For Team Black (which has a fly speed), grapple attacks, forced movement directly up, and then dropping the opposed creature for fall damage.
Damage from falling is not an attack and thus lycanthropes are not immune to it.
Grapple, fly, and drop: Can a Huge bird (STR 15, <1000 lbs) really fly off with a Gargantuan Brontosaurus (>30000 lbs)?
This might benefit from a ruling allowing multiple grapplers to split the weight of an opponent when moving it: Can two creatures cooperate to carry a third to avoid the speed penalty?
Questions: As stated, would these three means work RAW to allow lycanthropes to damage one another?
Are there other possible means?
Optional rules are fine for answers as long as they are official options. I am especially interested in answers grounded in the Curse of Strahd setting. So, if you are going to suggest "arming themselves with silver weapons", it is a better answer if it explains within the context of the setting from where they will acquire these.