In A Boy and his Blob you take control of a guy with a pet blob.
He has to use the blob to do pretty much anything, and he does that by giving the blob (Blobert) jellybeans. Each flavor jellybean will make the blob turn into something different and occasionally useful. Except the ketchup flavor. I'm not even sure where you'd get ketchup flavor jellybeans, Jelly Belly doesn't make them. Though I can't imagine they'd be any worse than those Buttered Popcorn beans.
But, I've gone off on a secant.
Anyway, the ketchup bean is used if you lose your blob somehow and he can't get back to you. Throw the bean and he'll 'catch up' to where you are.
But, if you throw a honey flavor bean at your blob and before he finishes transforming throw a ketchup bean at him, he'll turn into a brick wall.
What does the wall do? Does it block enemy projectile chocolate kisses? Does it hold up a slowly closing door while you race to the other side to hit some control switch? Does it just look cool?
Unfortunately, the answer to all those questions is 'no'. The wall doesn't do anything other than waste a couple of jellybeans. But the masonry looks kind of nice, so it's got that going for it.