Mutagen: Increase base strength of a non-Gold unit by 4.
Spores: decrease base strength of a non-Gold unit by 4.
IMO this card is poorly explained. I didn't use this card for quite some time, wondering what is Mutagen or Spores effect. You guys need to have a better explanation, when people explore their deck.
You can see the detail on this page.
Thanks! That description was very helpful.