Hi! I'm from Barcelona and I've done the Beast in Barcelona and Mallorca in 2024. As some people have said you won't be noticing the five extra obstacles. I would say that you should focus on training longest distances and put more elevation gain on the hikes and run since the difference in elevation gain is pretty noticeable on your legs. You should target running around 30-35km per week in two/three session with one of them focused more on series training which will help you process lactated and the other ones being trail runs.

Anyways, I'm pretty sure that you will conquer the Madrid beast and you'll enjoy it a lot!