They can inflate and then they can do three things, do a huge jump that will deflate them, float/glide, and do a knockback attack that is similar to the diplodocus' only attack. They can also seat more than one person at a time
They have a damage resistance when inflated, so use a snow owl to freeze and deflate. After latest update, they can no longer be picked up or hit with bola. Heavily suggested to clear area of hostiles before KO. If timed right, you can keep gasbag in same area while tranqing by alternating freezing and shooting.