Butters sees something she wants, but cannot quite reach it from where she is. So, naturally, she figures out a relatively simple and non-convoluted solution using the nearby things at hand.

By the way, yes, that's the same Mew kid I drew a few pics ago. This is how it happened. You're welcome.

Edit: In case you guys haven't figured it out, this is, in fact, a TF parody, where a guy gets transformed for absolutely no viable reason.

Indeed, Butters had many methods to get what she wanted, and she displays several of them throughout the animation. Then, even after changing the kid, she had no actual reason to because she didn't actually utilize any of the additions (before you argue, the paw pads actually made gripping the flowerpot more difficult and awkward, so it's to the opposite effect). It was purely to make her slightly more comfortable and familiar with the machinations of a body to do a simple mundane task that took less than ten seconds.

In other words, this is probably one of the most unnecessary transformations you'll ever see in a one-minute gif. You're welcome.