Here is a funny idea i came up with in SST yesterday.
There could be a 2 point alien, called a shadow. Avalible at s1, the shadow could move about, and then blend into the environment, and act like a trapdoor spider. The alien could grab an human with its toung, and pull them into its stomach, where they get damage from acid, at about a marauder claw damage and rate. The human could shoot the inside and hurt the alien, or drop a grenade inside, and the alien would have no where to run, seeing as the grenade was inside it, and it would blow up in a shower of death.
Not serious, but it would be funny.