I would have real rewards and punishments, not marbles and time outs.

Won't go to bed when asked? No long story. Goes to bed promptly, two stories.

Wishes you were dead? Be dead and don't play with him.

Stop playing games if they won't follow rules or fight.

If they choose to squeal like pigs, they can live outdoors like pigs.

If they eat all their meal (assuming you make food they like), they have pudding.

I have a very strong willed, but also now very empathic and considerate 7yo. Without "breaking" or "destroying" his leadership skills, but instead by adding good people management and team building skills.