Your eyes are accustomed to the dim swamps that your kind reside in. You can see 40 feet in front of you in dim light as if it was bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

Due to your hydra ancestors, if one of your heads takes slashing damage equal to your AC+your constitution modifier, it will be chopped off. When a head is gone, if you haven’t taken any fire damage in the past turn, your head will grow back, but instead of one head, it will be two. But, if you end the turn with 0 heads, then you die immediately with no way of revival. If you have more then 9 heads, then they will begin to fight amongst themselves, dealing you 1d6 piercing damage per 10 real-time seconds they are fighting. You cannot stop them from fighting, you must wait for one of your fellow party members to cut however many heads off, and seal them with fire damage.
Hydra Heads:

As long as you have more than 3 heads, you have advantage on all perception and intimidation checks.

When in combat you have head tokens equal to the number of heads you currently have. When you are attacked by an opponent or other player, you can choose to give a head token to the DM in exchange for a reaction from the list below.
1. Put one head in the way of the blow and subtract your constitution score from their damage, but you lose the head.
2. Lash out at them as they hit you, dealing 1d4 piercing damage and locking on to them, making them grappled. If you’re still locked on to them on your turn, you can expend another head token to pump a special venom into your victim, petrifying them for up to one hour, depending on their constitution score.

Your constitution score increases by 2, and your strength increases by one.