The Hidden (1987)
Though as much as I love Kyle MacLachlan, I can't deny he has been in some bizarre films, thanks to David Lynch, no less. And if you ended up losing your mind from him as Paul Maud'dib from "Dune," this little sci-fi flick is REALLY out-there.
Taking a twist on those "Body Snatcher" films, but without the annoying pods, and brain-dead duplicates, the tale begins when some guy goes nuts and has a massacre at a bank (perhaps they told him he was overdrawn).
The mysterious thing is not the fact this guy goes berzerk, but the fact they plug enough ammo in him to kill him ten times over and let he still keeps going like the Energizer Bunny (but a bit more bloodier).
While in the hospital, we notice the man finds another body and opens his mouth where a disgusting alien form leaves and enters it.
He then revives and leaves.
Meanwhile Michael Nouri plays the detective who is stymied by this, esp. when Kyle comes onto the scene as an FBI Detective who doesn't seem like he's all there.
In a nutshell, Kyle's an alien after the evil alien who has a weapon that can't affect the evil ET when it's possessing a human (yeah, I can't figure out that one either). Meanwhile the evil alien keeps body hopping about until the final showdown.
Though back then, "The Hidden" was considered a sci-fi thriller, it now seems more of a B-Movie by today's standards..
Love to see this one riffed.