What are all the pokémon that we don't know the true appearance?

Question

Mimikyu under its cloth, genesect before team plasma modified it... EVERYTHING. All the pokémon that we don't have idea how they look like.
If it's appearence is hidden by other parts of themselves, i'm not counting. Saw the discussion on the comments and clarified :]

Comments

Cubone, Marowack, kangkaskan (has a baby but when bred it’s just a kangaskan?)
Most ghost Pokemon when they were alive probably,
Tangela and tangrowth, kabuto,

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I don't think Tangela and Kabuto really count because the thing you see is still their actual body.

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"Its identity is obscured by masses of thick, blue vines. The vines are said to never stop growing." - Gold/LGP/LGE
"Blue plant vines cloak the POKéMON’s identity in a tangled mass. It entangles anything that gets close" - FireRed
"It is shrouded by blue vines. No one has seen the face hidden behind this growth of vines." - DP/BDSP
"Many writhing vines cover it, so its true identity remains unknown. The blue vines grow its whole life long." -BW2/X
"Hidden beneath a tangle of vines that grows nonstop even if the vines are torn off, this Pokémon’s true appearance remains a mystery." - Sword
"It is cloaked entirely in blue vines, preventing any glimpse of its true identity. The vines impart a refreshing sensation when chewed—they’re useful as a spice." PLA
Yeah, when the pokedex entries repeatedly mention an unknown true appearance or identity, I think it fits the questions criteria

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That's like saying Piloswine's "true appearance" is the thing under its fur.

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I'd argue that this question is a bit open-ended as "true form" is not well defined. Genesect likely wasn't altered much, as Pokedex entries really only say that team Plasma just added a cannon on its back. The vines are clearly a part of Tangela, we just don't know what's under the vines. I wouldn't really define that as "we don't know what it looks like." It's like having to strip someone completely naked to know what they look like. That leaves us only with Pokemon that either used to look different, or that use foreign objects that aren't a part of them (Mimikyu) to conceal their real appearance.