Simplify the following text for a Grade 11 native English-speaking person.
Original: The games usually feature simple storylines ; the most common plot theme in the series being Bowser , the main antagonist , kidnapping Princess Peach , who the Mario brothers try to save during the games .
Simplified: The games usually feature simple plots ; the most common theme is that of Bowser , the main antagonist , kidnapping Princess Peach , whom Mario saves .