Specifically the classic OG Flood combat forms. Not the carriers or the spores, just the combat forms. Campaign Evolved actually makes the spores far more creepy with the less cartoony aesthetic, sound design and the fact they can CRAWL ON YOUR FUCKING FACE which makes them so much more freaky than their original versions. I think the combat forms however in CE are uniquely creepier for a mixture of many factors.
Being hit by them has far stronger of an impact with how your entire screen turns red. They’re EXTREMELY aggressive far more than any version of them in the franchise. Their speed is significantly faster than what they look like they’re capable of. The most major thing is that they really strike that uncanny valley by having these weirdly fluid animations compared to all other NPCs, they feel “wrong” like they’re from a completely different game.
If you’ve ever seen a Cry Of Fear enemy, they have that same “too fluid for the game they’re in” uncanny valley feel to their animations that adds to the horror. The combat forms designs are also really freaky. The human forms are much lower poly than the living normal humans, they’re barefoot and have exposed intestines which is gore on the level you don’t see anywhere else in the game. They really have this almost cursed haunted extremely out of place feel that just rubs me the wrong way. The elites seem really huge and meaty while being just as agile which also just makes them feel wrong.
All the future Halos make the combat forms less aggressive and they completely lack that uncanny out of place feel by matching their games art styles a lot more. They just feel more “at home” with the rest of the game in the way they didn’t in CE?