The list here seems more like a RDW deck and less a Burn deck. I feel like having less creatures would give you more mileage with your Young Pyromancers. If you must run creatures in burn, Guides, Lavamancers, and Youngs seem like the best choice. Too many creatures dilutes your instant/sorcery base. On the other hand, having too few relevant creatures means your opponents need less removal.
Taking another look at the list, he's only using 2 Chains. That seems like a mistake. I'd cut some sparks and marauders to make room for more burn spells. The best creatures base seems like:
3 Lavamancers
4 Guides
2-3 Pyromancers

