Spirit powers like Concealment and Guard have explicit limits on the number of targets that can be affected. What about others, especially sustained powers like Confusion and Engulf? Engulf is initially described on SR4A294, with extra on SM100 that says that engulf does not necessarily mean dragging the victim inside the spirit body. Material can 'appear' to use for the engulf, and can be sustained even if the spirit leaves the vicinity/LOS of the victim. Should that mean that the spirit can melee attack, and engulf, another victim while sustaining the engulf on the first? Or use confusion on one, sustain that, then use confusion on another?

The obvious difference I see, is that Concealment and Guard can affect multiple targets as a single action, while Engulf needs individual melee attacks, and Confusion needs individual complex actions.

I'd say it's quite possible to use a spirit power multiple times on different targets.
There's a catch, though: A spirit can only sustain a number of powers up to its magic. So if your force 4 spirit is already sustaining using Concealment and Guard, there's only two more sustained powers to be had.

That works for me.

Actually only one more then, since Materialize (to affect the material plane) is also a sustained power.

Any others want to weigh in?

Interesting point about Materialize being a sustained power. It makes sense too, that a spirit would need to spend a little effort "concentrating" to keep a materialized form.

Personally, I'd say this counts against the limit of sustained powers.