Mplus does not yet incorporate the partial credit model. See, however,
Huggins-Manley, A.C. & Algina, J. (2015). The partial credit model and generalized partial credit model as constrained nominal response models, with applications in Mplus. Structural Equation Modeling: A Multidisciplinary Journal, DOI: 10.1080/10705511.2014.937374
If the responses are mixed with dichotomous and polytomous data, for example, item 1 til item 6 are scored as 0 or 1, and item 7 til item 10 are score as 0,1,or 2. Is it possible to use the multilevel mixture Rasch model to analyze the data with dichotomous and polytomous scores?