Zam say's "Once during your opponent's turn". Meaning that you cannot cancel 2 powers with 1 Zam. Still good with Claydol. I wish it was a better attacker, tho. I hate using a ton of support-only
Magnezone is far slower as well, and can't hold it's own without Heatran or some other Pokemon helping it. Magmortar, however, can hold it's own without any help, and it sets up faster. Auto burn = 30 guaranteed damage at the end of your turn, and another guaranteed 30 at the end of their turn. Energy accel? From where? Do you mean Heatran's power? That's not really acceleration. Far better? That's a stretch. The only downside of not using Magnezone is the retreat issue.