I don't want to see Real Madrid's performance decline after Mbappe is in the squad, of course I hope for a better performance compared to the previous season. Mbappe is a free purchase which is expected to make Real Madrid even more feared in the world as a team, so it is hoped that all players can make a good contribution and work together throughout next season.
As long as Mbappe doesn't have the same behavior as he did at PSG then I think everything will go well and even Madrid will get better and I'm sure of that. Indeed, we know that Mbappe still has a selfish nature in him and that is a normal thing because he is a talented player and his age is still very young so it will be very difficult to control but on the other hand I am quite sure Ancelotti can suppress Mbappe's ego while in Madrid.
It's not that he have a specific behaviour , he's definitely good in making a goal happen which I think it's he's best role when he was in psg which means he gets a lot of chance with ball to make a goal happen but there's one thing about him he's not good In leading,he doesn't show any motivation when they are even down with one and if the person leading seem to be discouraged so easily then the team will surely collapse ... I think that's his only weakness.
About beign selfish , yes he's somehow selfish mostimes because he feels he could make that goal happen at that particular time he holds the ball.