From [this page] and other hints, I get the impression that Jagers are, literally, fearless -- they were bred to simply not understand the concept of fear. The fact that they are more or less immortal probably has something to do with this.
Jagers can apparently smell other constructs, as seen [here]. That could be quite significant, given Sarah's presence in the game as well as several other people in the Circus. Think carefully about the ramifications here.
Jagers seem, as a rule, to be incurable romantics. For instance, see [this] interaction.
Also, note that they never seem to call Sparks "Sparks". "Schmot Guys" seems more typical.
Jagers love [really big guns] almost as much as Mell does.
They are spectacularly impulsive, and rarely wise -- for instance, see [this page].
Injuries seem to be little more than an inconvenience, and are generally regarded as kind of cool; for instance, see [here].
Jagers can smell Agatha, as seen on [this page] and others. She smells very good to them -- it appears that their bred loyalty to the Heterodynes is at least partly pheromonal in nature.
General Khrizhan is the leader of the Jagers under Klaus' command, along with Generals [Zog and Goomblast]. It's honestly unclear whether they consider themselves to be serving the Baron, or manipulating him. Consider, for instance, the way that the Generals would clearly love for [Gil and Agatha to get together] -- implying that they would like to set up a dynastic marriage. This could easily turn into a good plot element for the Jagers.
While the Jagers are spectacularly impulsive, they do know that they are impulsive, and that this is sometimes a problem. As a result, they will often [counsel caution at each other]. Sometimes, they even listen.
It appears that they have few possessions, and don't worry very much about possessions, but they care very much about the few they decide to have. For instance, ["any plan where you lose your hat is a bad plan"].
At least some of the Jagers in game need to have orders. Lots of order. Confusing and complex orders. And we need to make clear that Jagers don't much like complexity. They need to have at least one opportunity for serious order-confusion schtick.
There is a bit of [circumstantial evidence] that the rank-and-file Jagers may not care for their own power structure. This isn't really surprising -- they're creatures of chaos, so imposed order seems like something they might not appreciate.
They refer to themselves in the collective as ["Jagerkin"].
Jagers do not much like Lackya.
Jagers are [touchy about their orphan status].
There is occasional evidence that Jagers will eat almost anything, even [bugs].
The Jagers consider Mechanicsburg to be [their home].
There are a [number of hints] that the Jagers are superlative trackers.
The Jagers all [have the hots] for Von Pinn. Now there is a fine opportunity for horrifying character interplay, if she's in the game. There's an implication that the Jager concept of romance [isn't all that different from the Klingon version]. It's [entirely possible] that Von Pinn shares the same attitude.
Klaus [is well aware] that the Jagers' first loyalty is to the Heterodynes. His power over them is tenuous, relatively speaking.
Jagers are [not susceptible to slaver wasps].
As of game time, most Jagers have been [kept busy in remote parts of the empire]. So our wild ones are among the few who are currently nearby.
A delightful touch: Jagers [use the term] "rhinohiding". Exact meaning is unclear, but it seems to mean pretending that a serious wound is minor -- close to the SCA usage.
"w" -> "v": "one" -> "vun"
"v" -> "f": "of" -> "uf"
soft "th" -> "d": "these" -> "dese"
hard "th" -> "t": "thing" -> "ting"
Trailing "ng" -> "n": "going" -> "gun", "breaking" -> "breakin'" Or, trailing "ing" -> "ink": "looking" -> "lookink"
"your" -> "you"
short "a" -> "e": "captured" -> "keptured", "clank" -> "clenk" Or, short "a" -> "o": "that's" -> "dot's"
Leading vowels gain an "h", Cockney-style: "okay" -> "hokay"
"st" -> "scht": "stupid" -> "schtupid"
"sm" -> "schm": "smart" -> "schmot" (also shows "r" sometimes dropped)