Paper Mario 2 Partners Help?

Question

I read that you can upgrade your partners twice, but how come when I went to Merlon, he only lets me upgrade the non-upgraded characters?

Answer 1

This is because Merlon doesn't know about the second upgrade himself yet. After Chapter 5, Merlon will tell you about a dream he had about a room inside Hooktail Castle. Go back to the room where there were spikes in the ceiling and the floor, after the room where you got the Paper-thin ability. At the far side of the room, there is a crack in the wall, use Bobbery to blow it up. Inside there will be a treasure chest. Open it to get the Up Arrow. Bring back the Arrow to Merlon and he'll fly up to his ceiling and discover an orb that'll allow you to upgrade your partners to the second rank. But you can only upgrade them to the second rank after doing the first rank, which requires 6 Shine Sprites to do. Hope this helps, good luck.

Answer 2

You have to upgrade the non-upgraded partners first to access the second upgrade