Here are my thoughts on crunch so far. This is sort of tailored to this situation: a barbarian who chose the curse. I like that it is mostly a penalty at first, but can evolve into something that will be very strong in combat (at RP cost).
Starting immediately
- Can communicate with wolves and dire wolves indirectly; can sense their emotions and communicate in feelings. Can attempt to give 1-word commands, with advantage to CHA rolls made to influence them.
- Horses no longer allow you ride them; other non-wolf/dog animals are uncomfortable around you.
- Will wake up away from the party in weird places, maybe the occasional blood stain, with no memory but having had "strange dreams." It should become very quickly apparent that this character should not be given watch, and may be a burden on the party as they decide whether or not to watch him as well. (This ends after the first full moon is over.)
During the first full moon
- Change into hybrid form is uncontrollable. As he is embracing it, he'll get a DC 13 Will save to try to regain control of himself; on a fail he won't control his character for an hour, and each hour he can repeat the save until he succeeds (or morning). He'll feel the uncontrollable urge to attack anyone he finds, although he'll only use his natural weapons when not in control of himself. This change lasts until morning and does not wear off.
- Full moons last 3 nights in a row. After the first night, if he succeeded at some point on the previous full moon check, he'll get advantage on the first roll to control himself. This will repeat every full moon, but when it isn't a full moon he isn't forced to change.
After the first successful control (i.e. once the player successfully rolls to control himself)
- He already had darkvision but would have gotten this in hybrid and wolf form.
- In a reversal from previous sources, I'm going to say that the curse can only be removed when it is NOT a full moon. It's too strong otherwise, especially for one who embraced it.
- I like the "level up your wolfiness" idea; as he continues to do wolfish (i.e. horrible) things, he will gain in werewolf power.
- Since he embraced it, and he's a barbarian, it will work as a barbarian rage: he can voluntarily change into hybrid or wolf form by using a barbarian rage as a bonus action. If he changes into a wolf, he gains the wolf form but no barbarian rage features, but he can maintain that form for a number of hours equal to his level. If he chooses a hybrid form, he'll gain the normal barbarian rage bonuses plus the bonuses and penalties listed below, and must continue to attack or be damaged, or he'll lose the change after 1 minute.
- Each time he uses a barbarian rage without transforming into a wolf or hybrid form, he must make a DC 13 Will save or transform into hybrid form. If he was already damaged in the same encounter, he has disadvantage on this save.
Wolf form
- Normal wolf stats, except he retains his mental stats. No equipment merge: everything falls to the ground. HP is treated like a druid shift.
Hybrid form
- No equipment merge: everything falls to the ground or is ruined, as appropriate. Gain 11 temporary HP (otherwise your HP is your own).
- You look more like the Wolfman from classic movies: super hairy, maybe a few inches taller, but not crazy different. With enough clothing and darkness people wouldn't realize you weren't a human.
- Gain bite and claw attacks (STR based, as the werewolf stat block, with same chance to inflict curse on bite). Your natural weapons are treated as magical for the purposes of DR (otherwise werewolves could never hurt each other).
- +1 to AC
- Your rage damage resistance changes to: you have resistance to bludgeoning, piercing, and slashing damage from weapons that aren't silvered.
- Each time you take damage, you must make a DC 13 Will save or make an opportunity attack against the closest ally or non-enemy. (This will be especially crappy since he is a wolf totem barbarian who gives advantage to adjacent allies.)
Hybrid form, empowered
- You look like the werewolves from the Underworld movies: you are a true hybrid-looking monster; you gain at least a foot or two of height and are nearly a large creature. No one would mistake you for a human anymore.
- Your rage damage resistance changes to: you have immunity to bludgeoning, piercing, and slashing damage from weapons that aren't silvered.
- Your rage bonus damage is doubled when you are in hybrid form.
- You gain the fighter's Second Wind feature, which can be used in any form. It is recharged immediately after transforming.