That makes no sense at all. As you yourself pointed out, why would a non'lynchable person need 1 less vote?
Here is what I found about Gengar's abilites-
Gengars have the ability Levitate. Levitate makes Gengar immune to Ground-type moves. This Pok?mon hides in the shadows. It is said that if Gengar is hiding, it cools the area by nearly 10? F. When there is a Full Moon, this Pok?mon likes to scare people by pretending to be their shadow. Then, Gengar laughs at their fear. Gengars are mostly based on being mean and evil by tormenting people and hurting them and overtaking them. It can absorb any surrounding heat, leaving a sudden chill. To steal the life of its target, it slips into the prey's shadow and silently waits for an opportunity.Gengar is also able to merge with and inhabit the shadow of another being.
(Nothing mentioned about invisibilty, though he could hide in the shadows.
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Interestingly, in Varun's last vote count (where he mentions Zorax requires 3 more votes), he showed Zorax's votes as 6.
Now 3 cases arise (acc to me)
1. There was an invisible voter who voted after that post.
2. There was an invisible voter who had voted before that post but his vote tally was not added, keeping his 'invisiblity' in mind.
3. Zorax requires 9 votes for a lynch. (1 less than the usual)