Who is Wafner?
Wafner is a Nazi soldier seeking to kill and even use captured soldiers and villagers in a secret compound that housed a lab with a sinister twist, and that's performing heinous experiments on them.
His intentions were to put it simply, abduct villagers (children included) and soldiers (mainly the US soldiers and maybe even kill them, whichever works best for these Nazi soldiers) and use them as live test subjects, which leads to grotesque mutations that makes them far less human. In other words, their intentions were to use the serums and turn them into super-soldiers, regardless of the consequences.
And Wafner here knows what's right and wrong, and chooses the latter in the end, because he sees other humans (mainly the villagers) as living lab rats, or shooting galleries. He's a Nazi after all, do you expect to feel sorry for him and his soldiers? Absolutely not.
None whatsoever to show. His voice is cold, his appearance is something to be feared of (whether he's been mutated or not), and he takes extreme joy in just playing mind games against his opponents (he's been shown to be beaten to a near pulp and still laughs at this in a spine-shivering manner).
As for Wafner himself, he's cold, ruthless and, to put an extent, a living nightmare, and is quite the rapist as well when he tried to rape Chloe, and shows no empathy either, as evident when he kidnapped Chloe's brother Paul for an experiment.
Not only that, he looks human at first, because he really IS human, but after a scuffle, a shot through the face shows what a true monster he really is with that disfigured face of his, especially after injecting two test serums into himself, which not only drives him mad, but soon turns into something to become truly terrified than the Bogeyman himself, completely devoid of normal emotions even. It just puts other horror characters with disfigured appearances like Freddy Krueger to shame (at least in my opinion).
Wafner has no supernatural powers, but with the serums injected in him, he becomes near invincible. He's been shot and impaled directly through his chest and STILL puts up a fight. Even shooting him in the head won't do anything except drive his murderous bloodlust over the edge to the point when he's more monster than human.
Simple, really. Abduction (along with inhumane experimentation, even though his fellow scientist did all that (forgot the name)), attempted rape and murder. He's a Nazi, after all.
Again, he's a Nazi, so therefore, he shows absolutely NO empathy to his victims and his opponents. This was also evidenced when he injected the serum in him, which completely eliminates any kind of sympathy in him, replaced with a true desire to kill, maybe even more abduction if he feels like it.
Wafner's evil intentions are akin to Red Skull, who is also Purely Evil and a Nazi as well, and because of his obviously evil actions, it's quite clear enough that he's fit to be Purely Evil, though that's entirely up to you people on whether he's truly fit into the Pure Evil category or not.
And Wafner's face says it all: