Can Imp invis be used on multiple targets at the same time?

I have a mage wanting to use it on total of 4 people in the group (3 plus himself)
I imagine it will require rolls on Fading but will spell even work that way? or is it a cast 4 separate times and maintaining all 4 spells? and if so what kind of penalty is that going to be?

Thanks in advance for answering the Noob Questions

Your best bet at it would be casting all 4 at once (splitting your pool for them) and taking all the drain with a +3 for each spell.

Why do I recommend doing it that way? Well, otherwise, you'll cast one, and sustain it. Then cast the second at -2. The third at -4, and the fourth at -6.

For a grand total of -8 to your dice pools while walking around with them sustained, unless you heavily invest in bound spirits/sustaining foci.

The rules for targetting multiple targets with the same spell at the same time is described on page 173 under the section Casting Multiple Spells.

Alternatively, you can also cast the spell several times in succession.

The first has the advantage that you'll only have to sustain one spell. The disadvantages are that you have to divide the spell dices, making the spells really ineffective (if you even manage to land a hit at all), and having to endure a higher drain for every additional target.

The second version with casting the spell many times has the advantage that at least the first targets will rather have a good concealment thanks to more hits allocated, but every additional target will get more unlikely and unlikely, as you get the -2 dice modifier for every spell that you have to sustain. Also, in the end, you'll have a -8 dice modifier. However, the individual casted spells might at least have potentially more hits than above.

A good idea would be to mix and match between the two. Cast the improved invisibility spell on two members at once, and then again on the other two, preferably at those who are naturally good on sneaking anyway.

Spirits with Concealment are your friend.
Spirits of Man that can aid in casting Improved Invisibility can help with the split up dice pool. It'd be split AFTER the extra dice but can add valuable hits.

Particle, you have that incorrect. You can cast multiple improved invisibility (ii) spells, but they are exactly that, individual spells.

For an example, we have a mage with who knows ii, has magic 6, spellcasting 6, willpower 6, and logic 6. They have 3 friends f1 f2 and f3 they'd like to turn invisible, as well as themselves. Option one, is cast the spell 4 times in one complex action, taking a penalty to the drain. Option two is to cast the spell 4 times in succession.

Option 1: Mage decides to cast the spells at force 2, and splits his dicepool of 12 (6 magic 6 spellcasting) into 4 sets of 3 dice each. Mage rolls 3 dice per spell, getting 1 success on average. Mage then resists drain for each spell. Since he cast 4 spells at once, each spell gets a +3 drain modifer. Mage resists ((Force 2/ 2) +1 +3) x 4 for the 4 spells. Simplified, he resists 1 + 1 + 3 or 5 drain per spell. So, mage rolls (6 logic + 6 willpower) averaging 4 successes on average. So he ends up taking 1 stun per spell, for a total of 4 stun on his track.

Option 2: Mage decides to cast the spells successively. Mage casts on himself first. Force 2 for comparison to option 1. 12 dice to cast, 4 hits on average, only 2 count. Drain is 2. 12 dice to resist drain, 4 average, 0 damage. Next, mage casts on f1. 10 dice to cast (-2 for sustaining the first one), average of 3.33 successes, but only 2 count anyway. 12 dice for the drain of 2, average of 4, and 0 damage. Next up, f2, 8 dice to cast (-2 for himself, -2 for f1) average 2.66 hits, only 2 count. 12 dice for drain of 2, average 4 hits, 0 dmg. Last up, f3, 6 dice to cast (-2 himself, -2 f1, -2 f2) average of 2 hits, 2 count, 12 dice for drain, and 4 hits average for 2 drain, total 0 stun.

Comparison? Doing them in succession while you have the skills to eat the large penalty is better because your drain is much much less. However, keep in mind option 1 took 1 complex action to do. Option 2 takes 4 complex actions.

that's just plain silly. using theoretical averages is only reasonable occasionally. there is way too much room for variation to declare that over the course of 4 rolls, you will get a statistically average roll each time.

averages in random situations will happen *eventually*, but unless you're talking about arbitrarily large numbers, i don't personally feel that using the "average" roll to prove a point for in-game use is relevant (with the exception of discussing force 10,000 blood spirits and such, in which case the actual roll would likely come close enough to average as to not be significantly different =D )

You could also consider either obtaining an area version of invisibility or taking a hit of Psyche (reducing the sustaining penalty to -1/spell).

Dancer's suggestion is a good one, although it depends a fair bit on your character's personality.

Jaid is correct that the variance is quite high, although that doesn't completely belittle statistical comparisons. It does mean that things can go very wrong if you bank on the expected result to come up, however.

IE: With 12 dice, the average number of hits is 4, but believe it or not there's only actually a 23.84% chance of actually rolling 4 hits. You're actually more likely to get either 5 or more hits (36.85% chance) than you are to actually get 4.

That doesn't mean you can't assume 4 hits, however, just that you need to take into account the times when you roll 3 or fewer hits (39.31% of the time given 12 dice)

@Tarantula:
You might want to consider factoring where the character fails and needs to re-cast into those examples or, in your later example, use the system to trade 4 dice for a hit which allows you to guarantee getting the first few spells off as well as you want.

It's worth noting that if you only cast the spell at force 1 in the first example then you take no drain. As you're unlikely to get more than once success, why cast it at a higher force.