"Alright, men," Colonel Saunders began - she had long ago ensured that everyone was aware of the 'u' in her name - "This is your new favorite target." A distant picture of the strange alien appeared on everyone's HUD.
"As of right now," Major Leeds continued, distracted by how much he hated leading briefings, "if you see one of these alone - and they are usually alone - then you shoot to kill."
Captain Pletcher made sure that he was thorough when he explained things. "That means no warning shots. That means that you attack, if possible, before radioing for backup. You are to report the sighting while shooting, not after."
"I know that this goes against your training, but it's very important that you remember these things." Lieutenant Korrapati made sure that his troops understood that these orders were not given wantonly, but also the weight of the situation. "They are called temporal assassins for a reason. If you miss, if you wound it, if another sees you, then you will not get a second chance. They will unmake you. You will never have existed."
"There is some good news, though," Sergeant Patariki said as she wrapped up. She indicated the middle of the creature - it was about half middle, with six long, grasping appendages emerging radially from it. "Its brain is spread all throughout its torso - I don't have time to mince words with xenobiologists - and it needs the whole thing. Hit almost any part of this big, inert target, and you've got a dead temporal assassin. Aim for the middle; even if you're off-center, it should end up dead. Always look for seconds before securing the area. Always put another bullet somewhere else in its brain before letting Intel take over; we need samples, but we can't be too careful."
"Alright, now let's go kill some assassins, while we still exist," Private Jefferson said, per his habit of talking to himself. He wondered how he got stuck with the job of killing these things. As dangerous as the things were, shouldn't they have sent more people?