The Blob vs Clayface

In a cage! Environment is favourable to Clayface so that he doesn't dilute or dry up.

Stalemate? Neither can harm each other

Hmmm, I'd give this one to ClayFace.
While they cannot hurt each other physically (since the Blob is basically impervious to physical force, and ClayFace would simply reform after being hit) ClayFace does have a weapon he can use against the Blob.
He can suffocate him.
Basically saturate his nostrils with mud, and try to ooze down the Blob's respiratory system by force. Since it has been shown that ClayFace can squeeze through a crack he should be able to do the same to the Blob's rather sizeable nostrils.
ClayFace wins.
But for him to win the Blob would have to expire.

clayface via suffication..

damn! i didn't think of that! ... how about Clayface vs. Colossus? I think it's been establish that he doesn't need to breath in his metal form?