Hi everyone,
I have some trouble with the rules of Mentem and Group.
It says in the rules that Mentem doesn’t use Part, but size modifiers as usual.
If I want to boost Call To Slumber to Group is it then +1 or +2 to the spell lvl?
lvl 10 Call To Slumber
R: Voice D: Mom T: Ind
Still +2 magnitudes (+10 lvls). So a call to slumber for a group is lvl 20. (Most common spell doing this is "Scent of peaceful slumber" - although that is target room).
Thanks fore the reply, I have som additional question.
Some where in the book it says something about +1 in size, multiplies the targets by 10?
Is this only after you have boosted the spell to Group?
Or can you boost the spell with at +1 size modifier instead for Target and and then infect a Group (10 People)?
No, that'll just let you affect a single big brain.. perhaps a giants
If you want to affect a group, use group target ^^
and if you have a group target and want to affect more than 10 minds, use the size modifier...
Thanks everyone!! 
The size mod is a great way to gain "group" with +1 magnitude. But there are times when Target: Group is more appropriate.
Doesn't work. Size mod only enlarges your maximum target.
Group does a combination of that, and allows you to spread your size over several targets...
Yeah. In a rather frustrating quirk of the rules, anyone with "large" or "giant blooded" is technically 100% magic resistant to most formulaic T:Individual spells and effects.
Individual corpus spells will still nab folks with a +1 size IIRC and size doesn't matter to mentem. So large won't do much for you (in this particular respect) at all.
(That's from memory, I'll invoke serf's parma)
A Corpus Individual is size +1, so only Giant Blood shields you... from nefarious and beneficial spells alike (except Intellego). A magus with Giant Blood will have to bump his Personal-range spells by a magnitude too!
Yes, it does, but I did a terrible job of saying what I meant.
What I meant (but didn't communicate very well) was to agree that the size mod is a great way to make a Group x10 the normal size. I then wanted to make a comment that that is sometimes overkill, and a waste of that extra magnitude.
(For instance, while Mentem-effecting a group x 10 to be afraid of you would work just fine, trying to "read the thoughts" or "rewrite the memories" of that many in one spell could be problematic.)
But I didn't say that very clearly at all. 
And, yes, either way, Target = Group is first necessary.