It is one of the errated cards.
Q: Blastov's Flame Jets state “Mutate any Gruff” but this card is not a mutation, what does this mean?
A: This is another editing error, please ignore the phrase “mutate any gruff” on this card.
If you have any other gameplay questions, please add them to the comment section below. I will answer them in the comments, and include them in updates to the FAQ