Indo-Malayan mimic octopus
Now here's a cephalopod with a real talent. The first picture below is this clever Indonesian mimic octopus propped up above his burrow, keeping an eye out for food and danger; in the next picture, he's on the prowl, just relaxing in his natural colors.
Startle him, though, and poof, he transforms into a flatfish and swims away!
If he's worried more, he'll suddenly adopt the coloration and shape of a spiny, poisonous lionfish.
Aaaah! It's a banded sea-snake! Swim away!
But no, actually it's the octopus again.
And if you want to see these impressive tricks in action, here's a couple of movies. In the first, the octopus flashes stripes, and then turns brown, curls around, and swims off just like a flatfish.
In this one, he's tucked into his burrow with just two arms hanging out, doing a sea snake impression. Near the end, watch the fish swim into view, say "Yikes!"* and dart away again.
*OK, he really doesn't say anything, but you know he was thinking it.
Norman MD, Finn J, Tregenza T (2001) Dynamic mimicry in an Indo-Malayan octopus. Proc R Soc Lond B Biol Sci. 268(1478):1755-1758.