Shapechanger. The wererat can use its action to polymorph into a rat-humanoid hybrid or into a giant rat, or back into its true form, which is humanoid. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies.
Keen Smell. The wererat has advantage on Wisdom (Perception) checks that rely on smell.
Multiattack (Humanoid or Hybrid Form Only). The wererat makes two attacks, only one of which can be a bite.
Bite (Rat or Hybrid Form Only). Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage. If the target is a humanoid, it must succeed on a DC 11 Constitution saving throw or be cursed with wererat lycanthropy.
Shortsword (Humanoid or Hybrid Form Only). Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage.
Hand Crossbow (Humanoid or Hybrid Form Only). Ranged Weapon Attack: +4 to hit, range 30/120 ft., one target. Hit: 5 (1d6 + 2) piercing damage.
The Pied Piper
Sick Dude
I did the same for all but Zeleen herself. I ruled that it takes about a year for a wererat's full "gift" to manifest, so those turned within the last year only get damage resistance. Older ones have full immunity.
In a game that I was running that was focused on Illithids and Lycanthropes, these guys would form Secret Sewer Societies where they'd set up bombs, chemical weapons (some of which would turn the town into Lycanthropes themselves) and various other monstrous creations, and the party had to go through many moral dilemmas over it. Lycanthropy was appropriately hellish, slowly and agonizingly transforming your body and mind, and curing it was potentially unsuccessful, lethal, and guaranteed to be costly, so they HAD to go through those dilemmas. Forcing high-lvl players into situations where their power won't fully solve the problem is always fun, especially when you can get some really nice character development out of it.
Wererat? I hardly Know-rat
scary
Rats, Wererats, we're Wererats.
We pray at night, we stalk at night, we're Wererats.
I'm the big Wererat that makes all of the rules, let's see what kind of trouble we can get ourselves into.
Don't rats have claws? Then why doesn't it have a claw attack in its hybrid form?