Over the years, Marvel has dropped some right repulsive visitors on their denizens out of the sky. So I ask, not the most published, not the most famous, not the most powerful...
Which was the most gruesome, the most repugnant, the most viscerally menacing of all the aliens Marvel threw at Their Earth?
PS: Purely Divine/Demonic/Mystical Entities don't count. This is for creatures that are predominantly Space Aliens.