Critique - Alien

As always, love the bugs crawling out of the alien's mouth. :)

Let's look at the gun guy. He looks already really good, so let's be nit picky.
I feel like you could add a bit more weight to the gun. As the screen left hand lets go of it, I would lower the back part of the gun down. Even though the other hand is in the middle of the gun and could keep the balance even the way you have it now, I think it would be neat to see the effect of him letting go. You have it in there for a tiny moment but then the gun goes up again. It feels light because it happens so fast, first down then up, that quick jiggle makes it feel light.
Add one more pass on the screen left hand. It still feels a bit IK-ish. Look at the beginning till around x65. The hand goes up and down in a slow and even way, with the wrist keeping the same orientation, even though the body and arm is moving around. That just gives it away as being IK. Same goes for when the hand lets go off the gun. Go from x67 to 68. Gun butt moves away yet the hand keeps the rotation, I would rotate it down as it lets go.

I would make the "no" part during "I don't know." a bit faster and have it happen a frame or two earlier, it just feels a bit soft and a tiny late.

I like the last little expression change at the very end of the clip and the little eye darts. Also how he emphasizes "alien" with his body and arms. Overall there is nice detail work on him.

Now the lantern guy.

I would tone down the amount of eye darts at the beginning. To me the intensity is a bit gone and makes him unfocused. You could keep the one x10, but maybe try a version with no darts at all. I would go for an intense stare until "... it is.", so around x45 have an eye dart going from right to left (or left to right, up to you), but I would keep it to that, then have the head turn. Right now at x53 you got one to the left, then immediately down after that, little drift then up right before the blink and head turn. That's just too muddy to me. The ones after that are much clearer and focused.
Around x128, a few frames before and after, when he stops his head/body turn, it feels like there is a little hitch as he ends that turn. I can't pinpoint it, check your keys and curves (unless it's just a constant hiccup in my quicktime).
Check his left elbow around x76. As he turns around, the turn felt fast. I think it's mostly because of how the elbow gets tucked in after x72. Give that movement 3 more frames or so.
His right hand has a few IK problems towards the end. Check how the arm slows down towards x135. After that it drifts screen left to x160 in a very straight line. After that it goes back screen right, then down with an even wrist rotation, then back screen left in a straight line until x227. So that's a long section which needs more work to get rid of that IK feel.

But all in all a really cool clip!!

For those who haven't seen it yet, I really like the composition with the two guys left and right and the alien in the middle. There is also good back and forth attention grabbing between the two characters. It doesn't feel confusing, I always know where to look.