_Since there seem to be several, and the question is more or less asking for a (limited) list, let's make one! And let's make it a CW-answer to have everyone contribute._

_If you find another one, make it a separate answer to get voted on, then add it to this list._

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### Jigglypuff
The answer given in the episode, Jigglypuff as seen from above.

[![an image taken from the Pokémon cartoon series, showing a man wearing a blue cardigan with a yellow 'P' in it, pointing to a screen showing a Jigglypuff seen from above, proving it to be perfectly round][jiggly_s]][jiggly]

### Voltorb
One of the suggested answers in the episode.

[![a Voltorb, a Pokémon that looks like a Pokéball (a sphere with its top half red and its bottom half white) but with eyes, although it's not perfectly round from the angle it's shown][voltorb_s]][voltorb]

### Foongus
Foongus would be a trick answer like the one in the episode, since it only works when seen from above.

[![a Foongus, a Pokémon that looks like a mushroom, with a pink button nose and two black eyes on its stem, as well as appendages protruding from that stem, as well as larger circular hood; the Foongus is creamy white except for its hood that looks like a Pokéball, half white, half red][foongus_s]][foongus]

### Ditto
A Ditto is capable of transforming into any other Pokémon, so into any round one as well.

[![a Ditto next to a Voltorb (the Ditto on the left), two spherical Pokémon, both ; with the Ditto having retained its own face with small black eyes as opposed to Voltorb's expressive large eyes with eyebrows above it][ditto_s]][ditto]

### Diglett
A Diglett looks as if it could be quite round when seen from above, although it does have a nose that may poke out.

[![a Diglett, a Pokémon that looks like a brown earthworm with black eyes and a pink nose; the Diglett looks as if it might very well be round when seen from above][diglett_s]][diglett]

### Ghastly

A Ghastly is spherical as well, if we disregard its aura.

[![a Ghastly, a Pokémon that looks like a black sphere with big eyes and sharp teeth like a vampire, floating in a purplish cloud, its "aura"][ghastly_s]][ghastly]

### Sandaconda

Sandaconda, when viewed head-on, would give a spherical silhouette.
[![Sandaconda is a snake-like Pokemon with a big round "tube" surrounding its head.][sandaconda_s]][sandaconda]

### Drifloon

Drifloon is also a round shape, and when you remove the strings (or view from above like Jigglypuff) it could certainly match the image from the show.

[![Drifloon, a balloon-ghost pokemon that likes to carry children away.][drifloon_s]][drifloon]

[jiggly]: https://i.sstatic.net/vlFHx.jpg
[jiggly_s]: https://i.sstatic.net/vlFHxm.jpg
[voltorb]: https://i.sstatic.net/zMSAx.png
[voltorb_s]: https://i.sstatic.net/zMSAxm.png
[foongus]: https://i.sstatic.net/yaNSK.png
[foongus_s]: https://i.sstatic.net/yaNSKm.png
[ditto]: https://i.sstatic.net/oAuDX.jpg
[ditto_s]: https://i.sstatic.net/oAuDXm.jpg
[diglett]: https://i.sstatic.net/LLJan.jpg
[diglett_s]: https://i.sstatic.net/LLJanm.jpg
[ghastly]: https://i.sstatic.net/y3YlK.jpg
[ghastly_s]: https://i.sstatic.net/y3YlKm.jpg
[sandaconda]: https://i.sstatic.net/sd3QO.jpg
[sandaconda_s]: https://i.sstatic.net/sd3QOm.jpg
[drifloon]: https://i.sstatic.net/OAJ6i.png
[drifloon_s]: https://i.sstatic.net/OAJ6im.png