I absolutely adore nicknaming pokémon, I feel that it adds so much more personality to your partners. I personally chose names that I think fit that indavidual pokémon. For example, I named my Talonflame “Blaise” because it’s part fire type, but still unique enough to not be cliché. Hopefully I can help you do this with your pokémon.

Now, for your shiny Butterfree, I would personally choose a name that would fit perfectly, considering it must have been a long journey to obtain. A pokémon like that must have a name that’s both unique and stands out. Names that come to mind include Constance, Flora, Victoria, Adaline, or Florence.

As for your Porygon2, I think a math based name would fit, wouldn’t you? Perhaps Lateralus. “Lateral” is a part of the word 'Quadrilateral', which is a polygon, of which Porygon's body shape is made up of. Plus, it's a Tool reference. The “us” just turns it into a name. I’ve dubbed my own Porygon this, and thought it would be fun to share.

You’re totally not obligated to use these names, just thought that it would be fun to throw out suggestions.