Uhh, what's a "normal entangle attack" in whatever edition these came from? I'm not seeing that this really corresponds to the entangle spell or even necessarily a net. But, that said, I can go for something similar to what you have.
Well that's the problem, isn't it. OA2 is a first edition AD&D module that uses the
Oriental Adventures hardback's rules, but there's no "normal entangle" special maneuver in that book's Martial Arts rules.
The only specific rules for "entangle" attacks I can find in the core 1E rules regard magic items and spells (e.g.
entangle and the
rope of entanglement), both of which render entangled victims helplessly immobile. The Monster Manual says that Shambling Mounds can entangle a victim they hit with both attacks, but it doesn't give rules for what that entanglement actually means.
I'd like the victim to be able to escape by dropping the weapon, I'd rather the victim not be able to use somatic components (either in addition to or instead of the Concentration check), and I think it should be harder to establish than a touch attack. Oh, and since the attack is specifically entangling the weapon, I don't think a failed attempt to break out should disentangle the weapon but not the opponent. At the very least, it should be a melee attack since the veils aren't that long, I think. What about this as a compromise?
We seem to be heading at this SA from opposite directions, don't we. I'm pretty sure it's supposed to be an "entangled
plus weapon trapped" ability, not just a "ensnare weapon" ability.
There already is a 1E OA maneuver that traps an opponent's weapon and can be escaped by simply dropping the weapon - it's called Weapon Catch. If the writers of OA2 wanted it to work like that they'd have just used that manoeuvre, not created a new "special attack". (Incidentally, although it's called "Weapon Catch", that OA maneuver allows the attacker to catch an opponent's limb instead of their weapon.)
There's nothing in the original description about being able to escape the entanglement by simply letting go of the weapon, so I don't favor the "drop your sword and you're free as a bird" approach you propose.
The original description of the "Entangle Weapon" special ability specifies the opponent can free their weapon by making a strength save, but it doesn't say whether that also frees them from the "normal entangle attack" - whatever the heck that's supposed to mean. I can accept it can go either way, but would prefer to keep it so the victim can be "regular entangled" or "entangled plus bound weapon/limb" as it adds more variety to the combat.
Still, if necessary to break the impasse I'd be OK with it being an "all or nothing" escape. We still have to decide what action this requires. I'm visualizing the effects as being similar to an
animate rope spell (since it's an animated veil), which requires a full-round action to escape from. I considered adding a "lesser escape option" to free only their weapon arm as a standard action (like escaping from a grapple), but that seemed over complicated.
Preventing the target using spells with somatic components would be OK by me, and I agree it ought to be a melee touch attack. I'd rather not make it a melee attack, though.
I'm also starting to wonder if Multiple Actions is a bit much with an ability like this. Entangling 7 enemies at once would be pretty bad.
They're supposed to be a dangerous challenge to an entire party. They need to be able to multi-engage opponents to be effective. It should be possible to tweak the damage/break DC/escape action so that they're not overwhelming.