General Mills' Monster line of cereals expanded by 1 in 1973 with the addition of Boo Berry, which is a play on, of course, blueberry. They simply substituted blueberry flavoring for strawberry (Franken Berry) or chocolate (Count Chocula), as if the kiddo's wouldn't know the difference.
Today, the Monster cereals are kept in limited release, available only during October, instead of being year-round as they were originally. Considering that some stores charge as much as $5 a box these days, maybe it'll help the parents' wallets.
Anyway, here's the debut of Boo Berry, who floats in as Choc & Frank (both voiced by Bob McFadden) are doing what they do best---argue. Boo's voice is done by---who else?----Paul Frees, doing a Peter Lorre mimic.