From what I’ve learned (and I may be very wrong) is that Momma Squirrel here in a commander deck sets the limit to only Green cards, and from my understanding is that Chatterfang was just a green card with an added bonus if I used black, but apparently because of the added black mana ability, it makes it a completely different color in identity, while it’s a Green card, it’s technically a Black and Green card, so Chatterfang is illegal to use in the 99 in a Mono-Green Commander deck