Simplify the following text for a Grade 5 native English-speaking person.
Original: In Super Mario Bros. , the player controls Mario ( and in a two-player game , a second player acts as Mario 's brother Luigi ) as he travels through the Mushroom Kingdom in order to rescue Princess Toadstool from the antagonist Bowser .
Simplified: In Super Mario Bros. , Mario goes in the Mushroom Kingdom . There he must save Princess Toadstool ( later Princess Peach ) from Bowser .