6th Gen team

can some one help I need more pokemon what should I get gengar or charzard

Without any informations on your targets for your team. balanced? bulky? and so on. What other pokemons do you already have on your team? Are you planning to play Singles, Doubles, Triples....and so on ;-) THEN someone could help you, but the question "should i get gengar or charizard" seems a bit less.....

Salute!

What's the rest of your team? Depending on what else you have one of them may be a better choice than the other.

As Nah said, it's best to list your team since it will help us give you constructive advice. Out of the two Pokemon you're considering, both have a Mega Evolution with a Mega Stone that's easily obtainable in the game, however take into account that Charizard has two Mega Evolutions that have very different playstyles between the two, with X being a physical attacker and Y mainly being special.

Mega Gengar on the other hand is a fast special attacker and hard to outspeed for many, although it does come with a downside of losing Levitate for Shadow Tag, making it susceptible to Ground moves.

If you already do have a fire-type on your team, then I'd recommend Gengar, and if you're already carrying a ghost Pokemon, I would likely go with Charizard. In-game, I believe it's best to be utilizing a wide variety of types rather than a select few.