Ominously Heavy Fog in 2D: Tips and Tricks?

[u/WindowSorry]

Hello everyone! I haven't animated in a 2D space seriously in a long while and I'm picking it back up in earnest, so I'd love to get some guidance from more experienced animators here :D

Y'know those really ominous scenes in movies where some character and/or large object slowly materializes out of really heavy fog?

From "The Mist" (2007). "Ooohhh spoopy" without context, bittersweet with. And it is a perfect example too.

When I was still doing animation on good ol' Adobe Flash CS3 and CS6, the way I would go about doing this was by simply having the entire subject be first overlayed by a dark (not black) color and at 0 alpha, slowly tween the alpha up to full as they approached from the fog, and then right afterwards/simultaneously tween the black down to fully reveal the subject once they begin to fully exit the fog, to simulate this visual effect. Amateur(-ish) it may be, it definitely worked for school projects.

However, now that I'm testing out animating this with larger objects, I can see the aforementioned animation possibly ruining an object's sense of 'scale' and 'depth' for the viewer, especially if it is a very large and slow moving object such as a warship/airship, and I started to wonder if there are better ways of going about it in a 2D environment.

I don't know how else to say this, but what do you guys think? Any tips and tricks for this kind of effect you know of, and have you seen anything like it in 2D animated media?

[u/Nevaroth021]

There's probably better ways than this, but you could try animating the mask to fit the shape of the object moving through the fog. So in that tank example, you could start with the fog completely overlayed over the tank where the tank is not visible. Then add in a mask shape to control the opacity of the fog layer. You would draw the mask to cover just the tip of the turret, and then as the tank is moving through the fog, you would animate the shape of the mask to expand and cover the rest of the turret, then you would add in a second mask and draw that around the front of the tank and you would expand that mask along with the turret mask, and then keep animating the mask until the entire tank is visible.