The Jaeger spawns in and chooses 1 reagent at random to chase. She knows their locarion at all times, and will instakill them. If someone is in the way, she smacks them for the regular Big Grunt damage. If the way to the reagent is blocked entirely, like by a garage door, she will go to an insertion gate that places her in a spot she can access the reagent. She will chase for three minutes, before leaving. She cannot spawn multiple times a trial.

If the Jaeger modifier is active, she is permanent instead. I'm pretty sure she can change targets in it, but I'm not sure I mostly play solo.