Использование DELIMITER
до и в конце партии.
DELIMITER $$
CREATE DEFINER=root@localhost EVENT start_game ON SCHEDULE EVERY 3 MINUTE STARTS '2018-05-05 05:50:07' ON COMPLETION PRESERVE DISABLE DO BEGIN set @game_id = (select id FROM tbl_game where game_status=0 ORDER BY id ASC LIMIT 1);
update tbl_game set game_status = 1 where id = @game_id;
END $$
DELIMITER ;