that's a good question - am inclined to make it both, mainly for the reason that (like with other lycanthropes) they're in hybrid form 99% of the time when in combat - although another part of me thinks it might be good to reserve for snake form only so there is some advantage to being in snake form.....but leaning to the former (both).
A possible solution I came up with it giving it two tail-based attacks. A tail-whip that's just regular melee attack and a constriction attack where the weresnake is wrapping its whole body around a victim and restraining them.
Like so:
Constrict (Snake Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage, and the target is grappled (escape DC 13). Until this grapple ends, the creature is restrained, and the weresnake can't constrict another target.
Tail-Whip (Snake or Hybrid Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage.
Alternatively, using
Constrict in Hybrid Form hinders it in some way. Maybe it prevents it attacking with its shortsword or hand crossbow because its hands are occupied strangling a victim, or it can't reload its crossbow once its fired because it's too busy to properly use the Loading property, or perhaps it can only target the creature it is grappling? (Meaning it can still make shortsword or tail-whip attacks, but must attack the restrained target).
One of the following would do the trick:
Constrict (Snake or Hybrid Form Only)[No Weapons]. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage, and the target is grappled (escape DC 13). Until this grapple ends, the creature is restrained, and the weresnake can't constrict another target or attack with its shortsword or hand crossbow.
Constrict (Snake or Hybrid Form Only)[No Loading]. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage, and the target is grappled (escape DC 13). Until this grapple ends, the creature is restrained, and the weresnake can't constrict another target or reload its hand crossbow.
Constrict (Snake or Hybrid Form Only)[No Other Target]. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage, and the target is grappled (escape DC 13). Until this grapple ends, the creature is restrained, and the weresnake can't make melee attacks against another target or reload its hand crossbow.
Tail (Snake or Hybrid Form Only)[No Ranged Attacks]. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage. If the weresnake chooses, the target is grappled (escape DC 13) and restrained until the grapple ends. Until this grapple ends, the weresnake can't make melee attacks against another target or use ranged weapons.
Hmm, the
Tail-Whip and
Constrict have the same combat numbers apart from the grappling stuff, so we could combine them by making the grappling optional.
Like so:
Tail (Snake or Hybrid Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) bludgeoning damage. If the weresnake chooses, the target is grappled (escape DC 13) and restrained until the grapple ends. Until this grapple ends, the weresnake can't make melee attacks against another target or reload its hand crossbow.
The above is based on the "Special Edition"
Constrict [No Other Target], but it's be a simple matter to tweak it to another of the suggested constrictions.
Any of those take your fancy?