Which part of the Marketing mix has changed in the recent years? Which ones present big challenges today's marketers?

Promotional Strategies has changed mostly in the recent years because of the advancement in Digital Marketing Techniques. Advertising through E-Marketing and Social Media is much cheaper and also more effective because the marketer can easily focus on the specific target market. 

I agree with the experts answers. Thank you.

Marketing automation tools are a blessing but also creates new challenges. You now can almost do every kind of action via a tool. But it's a challange to keep everything in line and in order and not to loose the overview of all your management tools. Sure you can work more efficient and have faster and better results but it also creates more tension and demands more focus and time and work management skills.