In action, Marc generally kicks ass and can't be killed by bullets...sort of. As the film progresses, his powers weaken. It's just a shame that someone with actual acting range isn't around to convey the emotion involved!
Oh and there's a sub-plot where the teenager wants to sleep with Dacascos. You realize that you're trying to f#%k an alien Scarecrow, right?!?
As the biggest 'star' here (by virtue of being in Titanic), he is quickly written out, setting up the fight between Dacascos and his former-girlfriend. He wins. Afterwards, he risks the portal to go home, but...
In a post-script, he fights more alien terrorists, setting up a sequel that nobody requested. The End.