A Charismatic Human is a Human player whose lynch vote counts as two.

Variations

If insta-lynch is ON, the presence of a Charismatic Human forces the host to decide whether they change the number of votes needed to insta-lynch. Is it still based on the number of players in the game? If so, the Charismatic is more powerful and can stay hidden for longer. If it's based on the number of votes in play, the Charismatic is weaker and (in a mystery game) their presence can be exposed quite early in the game due to mismatch between the stated player count and the insta threshold (for example, insta being at 7 votes with 11 players alive instead of the normal 6, because with 12 actual votes in play, 6 is no longer a majority.)

Utility and Balancing

In most games, a Charismatic Human is a middling to weak role for the Humans to have. While usually the host will keep the lynch rules as normal and obscure the Charismatic Human's double-weight vote, it'll be immediately obvious that there is one once, say, a player is insta'd at one vote below the normal threshold; this lets the Wolves know that someone on the wagon was Charismatic, and as this possibility becomes more and more likely the further into the game the CH lives, they usually have a small pool of potential candidates to pick from. This problem is defused if insta-lynch is OFF, however, and in a game with significant vote-manipulating roles, this is often the case.

As a Human role that has an outsize influence on who dies, the Charismatic Human suffers from the same unpredictability as the Vigilante. If they only use their extra vote to lynch fellow Humans/Town, they're a detriment to their team; if they only use it to lynch Wolves, they'. Actual play by the person who draws the role can fall anywhere between these extremes. In addition, while the Charismatic Human can prevent their team from losing if the Wolves make up 50% of the players during the Day (since they do not control 50% of the vote), this requires them to actually make it to that stage, and typically only players who are deemed advantageous to Wolves' win chances survive that long, so this may require the Charismatic to play sub-optimally earlier in the game.

A boost to this role that can mitigate these issues somewhat is to make the Charismatic Human be able to toggle their ability on and off. This allows them to stay hidden until their extra vote is actually needed, and is strongly preferable if you want to keep instas on the table.

Furthermore, a Charismatic Human in an Alliance can be a powerful asset in the right conditions. The ability to close ranks more effectively around a prime Wolf candidate, or to veto a misaimed wagon on one of your Alliance-mates without having to claim, should not be underestimated.