The general contract in video games is that almost all of them will throw menacing, violent enemies at you and in return you’ll have the means to do away with them and journey on forward.
Not always, though.
Sometimes games don’t let you fight back at all, or sometimes you can fight back but it’s all for naught because said enemy can’t actually be killed. This is particularly common in horror games, but unkillable enemies can be found in plenty of genres as this list shows.
Just to get ahead of this one, there's no Alien from Alien Isolation on this list. Of course our Xenemorph buddy applies but I thought it was too easy so we’re going to give ten other enemies a go this time around.