So, you can definitely use the sentries Toxic mentioned a little while ago for aliens, if that’s what you’re referring to.
For the ships, I’d do some barrier art! Then, copy the ship barrier art a bunch of times in a path and hide and show them every half a second, so it looks like they’re moving.
To make them spray toxic gas, I’d also use barriers for that- tint the players screen green and also add little circular green barriers animated moving down.
I found this, does it help at all?