What size are you talking? What's the consistency of the mud? (gravy, pudding, etc) how deep does the mud go before you get to firm ground? Is it on a slope? (Uphill or downhill side?) can you post pics and dimensions of the area? Drainage is usually the critical factor in remediation of muddy areas. If it doesn't drain the excess water away then adding anything else will just make more mud. The smell is a secondary effect of the standing water, if you solve the first problem the second should be corrected also.
