1. To render something awkward, confusing, and disorderly; to obscure or obfuscate something. A noun or pronoun can be used between "muddle" and "up." Often used in passive constructions. The introduction of new tariffs is likely to further muddle up the already complicated relationship between the two countries. They muddled the contract up with all sorts of misleading, cryptic language. Our roles within the team have become so muddled up that we've largely given up the idea of job titles.

2. To mix something up (with something else). A noun or pronoun can be used between "muddle" and "up"; often used in passive constructions. They look so alike that I always muddle up their names when I see them. I must have muddled the data points up when I was entering them into the system.