Blood stains

[Yankes]

i think that would be fun if solders/aliens leave blood stains on ground when they are wound or when they are hit (of coarse different colors stains :> )
you could track wounded ones by looking on trace they left behind.

only problem with that is stains should be updated only when you unit see them.

[AlienRape]

So what colour will alien blood be then?

[Volutar]

There are blood colors showed on autopsy images. Some of them have green blood, some purple... But i doubt it possible in sprited oxcom version, because it will require huge engine rework and lot of "blood" tiles.

[Yankes]

not if we treat blood like items, then we would need only couple new sprites for every blood type (and maybe size).
alternative create new layer over floor (and under walls, items and objects) that will be used to draw blood (and oil form tanks ) 

[hellblade]

Three thumbs up for blood stains after corpses are moved away or for critical wounds.

What would be even better, is blood trails for aliens and humans alike.  Though this would mean adding critical wounds to aliens.  Trails would add a nice addition to gameplay.