Just watch Paranormal Activity: Ghost Dimension. Don't watch it, it's really bad. They use that Venom from Spiderman symbiote slime effect. Like living goo and stretches out and condenses.
How do you make that in Hitfilm?
Hoo, boy, in short, that effect is kinda out of Hitfilm's pay grade. You really need full fluid and physics sims for that. I am certain some interesting ideas for approximations will come up, so we'll figure out something cool.
Well the first thought is the Blender fluid sim and the Blender to HitFilm script.
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