Tainted Yoshi

Yoshi spent the first half of chapter 2 tainted by the Spider as a side-effect of his attempt to understand the Spider's motives during the party's meeting with it at the end of Chapter 1.

The taint was removed (replaced) by the Fox, who appeared as Sakushi in Truth and Beauty. Yoshi spent the run dazzled by the Fox, then settled in to a Fox-touched personality. Hiro took advantage of the opportunity to get Yoshi to update his wardrobe and get a makeover. Master Zhou, already preparing to help Yoshi purge the spider taint, whisked Yoshi off to see Master Kwan, who, with Tara Shien, led Yoshi through a cleansing meditation that allowed him to shed unwanted influences on his personality.

As of Phoenix Hearth, he is untainted (though slightly Foxier than before and better-dressed) -- until he hits another Great Spirit with "Why do you do this?"

In The Eighth Name Yoshi gets covered in a double dose of spider goo, which apparently requires spiritual healing to remediate, rather than just soap and water.