Thomas asked about how size works in JAGS.
There's a complex story here--but rather than doing what he asked (explaining how the rules used to work) I'm going to try a quick-hit and show the current rules. Here are two graphics that show how size is now purchased:
For getting bigger this is the formula: decide if your character commonly uses an edged weapon or not (this includes bio-weapons) and if so, go with the Armed numbers. If not, go with the Unarmed numbers. The first 8 points (or 4 if you are just buying a half-level) use the L1 numbers. After that, use L+.
I realize this isn't fully easy to understand--but hopefully it's more clear than the original rules. I'll do an example later when I have more time.
To be smaller:
A couple of notes:
1. Size is something many RPGs do very strangely. It's usually possible to be quite big without having the damage or defenses one would expect. In other cases there's simply no good provision for it.
2. There has to be some ancillary data around "how big does JAGS think an elephant is?" so you know if you are buying multiple levels if you are in the right ballpark. We'll provide that in the book. Originally our approach was to say "You decide 'I want to be as big as a horse' and then buy that level of size." It was good for some games and not so good for others. That's one reason why the rules are confusing.
3. There is another trait called "Monster Size" that gives ADP instead of DP--this is good for making monsters that'll fight a horde of lower-damage PCs since it doesn't jack the monster's Minor Wound score up so high they can never score one. I'd use it for dragons in games where I wanted huge dragons that a small group of relatively 'normal' characters had a chance to bring down (also note: the way JAGS performs when you can't score a Minor Wound number is a lot of the target being endlessly Stunned and Dazed for a long time--being "on the ropes" for several Rounds. This might be dramatic once in a while but would get old fast as a staple--hence the need for ADP).
Edited: Here is the size chart. If you hit one of the sizes listed you get the effects on the table (including the to-be-hit modifiers and CON bonuses). There are some more rules around this (the TBH modifiers are NOT treated like AGI modifiers ... and two really big things hit each other normally rather than at huge pluses--so there's some special cases there--but this will get you started).