Alien - 13 Halloween Costume Ideas
Alien costumes split between two approaches, playing the alien itself, Zoidberg's crustacean design, Megamind's big-headed blue look, the Predator's full creature build, or playing the humans who deal with them, like Ripley or the Men in Black agents.
Skin tone and texture carry most of the alien-creature builds, prosthetics and body paint matter more than clothing. For the human-side costumes, a plain tactical or utility outfit is usually enough.
Either works, check which one you have the time and budget for, the human side is usually far simpler to build.
The creature-style ones usually do, body paint and simple prosthetic pieces go a long way.
A mix of both, it spans genuinely tense creature designs and much lighter, funnier takes.