We are beginning a Curse of Strahd Campaign and one of my players wants to play a Ratman. I'm afraid that giving him lycanthropy at level 1 might be a bit overpowered so I toned it down and added some extra fun little abilities.
Ability Score Increase. Your Dexterity score increases by 2.
Size. Ratmen stand between 3 and 4 feet tall and average around 90 pounds. Your size is Medium.
Speed. Your base walking speed is 30 feet.
Darkvision. You have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.
Disease Resilience. You have advantage on saving throws against poison, you have resistance against poison damage and you are immune to disease.
Infected bite. Due to your life in the city's sewers, you have been infected by a number of horrendous diseases that have affected your physiology. You have a bite attack that deals 1d4 piercing damage. A creature hit by this attack must succeed a Constitution saving throw against a DC of 8 + your Constitution modifier + the amount of piercing damage inflicted by the initial bite. On a failure, the creature takes poison damage equal to your Constitution modifier and cannot be affected by any healing effects. On a success, the creature takes half damage and suffers no addition effects. The creature can repeat saving throw at the beginning of each of your turns. On a success, the effect is removed, however if the creature fails three times the effect lasts until the creature take a short or long rest (creatures immune to the poisoned condition are also immune to this effect, but still take the poison damage. Creatures immune to disease take nothing but the piercing damage).
Keen Smell. The Ratman has advantage on Wisdom (Perception) checks that rely on smell.
Natural Claws. Because of your claws, you have a climbing speed of 20 feet. In addition, your claws are natural weapons, which you can use to make unarmed strikes. If you hit with them, you deal slashing damage equal to 1d4 + your Strength or Dexterity modifier (your choice), instead of the bludgeoning damage normal for an unarmed strike.
Rodent Nimbleness. You can move through the space of any creature that is of a size larger than yours.
Languages You can speak, read and write Common and Undercommon.
The Infected bite preventing healing effects was specifically requested by the player so I'd like to keep that if possible, though rewording and balancing is fine of course.
If I need to be more specific about "Balanced"
Is this more or less powerful than a Wererat at level 1?
Have I given the rat too many abilities and if so which ones should I change or remove to balance things? (maybe a vulnerability)
Should the Ratman be a small creature? (my player doesn't think so but I do, maybe make it small but still have 30 ft movement speed cause there reactionary, quick and nimble for there size)
I'm tempted to add an ability similar to a toned down Alert feat or Cunning Action to make the race seem more jittery and on-edge but I think that might be pushing it a bit too far, Do you think I could add one more ability without tipping the scales?
For "Infected Bite" should I keep the "plus the amount of piercing damage taken during the initial bite" added to the DC or just make it "plus your proficiency bonus"?
Does the "Infected Bite" ability make sense or is it too wordy?
And most importantly, Does playing as an anthropomorphize Rat (or any more animalistic creature) in Curse of Strahd specifically, have any inherit unfair advantages/disadvantages?