Inferno tactics.

How is that possible? He saves everyone, but not so much for Inferno.

Inferno has good speed. Against medium and slow units, slowness isn't that necessary. And against fast units, you can sometimes manage with just regular slowness. But it definitely helps. And if you're using any potions, the curse looks much better in them. We fight in melee combat because ranged units are weak, and if needed, we can hold back any monsters with a single spell. The demons in Inferno also have good speed.