It's hard to think of an alien weapon that wouldn't behave like a human weapon. Screw it, just give'em a Terror-Site only weapon that shoots a deadly parasitic virus that slowly drops your health and stats each turn, but surely, once you're hit, you'll die a painful death in a few turns and you won't survive even if the game ends on the next turn.
Any operatives right next to anyone infected will also become infected as well, but it won't kill them, only drop HP by 25% to 30%, any operatives a tile away and around the infected may have a weaker drop in health, 1%-%5. You could make it worse
Terror only, since the purpose of this weapon is to cause chaos. Any civilians infected by this deadly virus will attempt to run toward an operative to(unknowingly) infect them as well.
After discovering this deadly weapon, you'll have the option to research a vaccine (tiny one-slot item that weighs nothing):
- Your Scientists will quickly create a vaccine that will remove the dreadful pain, so stats don't drop and you'll take longer to die. You might survive the whole mission, but you will die at debriefing.
- You Scientists make a critical breakthrough. This new vaccine will cure you, but it will knock you unconscious for the rest of the Mission, so taking this vaccination will depend on how much you need that operative in battle.
- Finally your Scientists will perfect this vaccine, with no side-effects. Upon taking the vaccine in base, you will be immune with no need to carry a Vax A, B, or C, but only to assist civilians that run toward you in pain.
Here's a way to prevent an exploit. You're not allowed to take more than one vaccination. Like say you take the first vax to continue fighting on, then before the mission ends when you're not needed anymore, you take the second vax to live and go unconscious. You will die if you take more than one vaccination. If you need a name, call it Vax
Next thing is the, I forgot what I was going to put here. If you're interested I'll try to remember.