$\lambda$-Griffiths polynomials: Bispectrality and biorthogonality

We introduce a generalization of bivariate Griffiths polynomials depending on an additional parameter $\lambda$. These $\lambda$-Griffiths polynomials are bivariate, bispectral and biorthogonal. For two specific values of the parameter $\lambda$, they become orthogonal. One of the value is related to the usual bivariate Griffiths polynomials, while the second value produces new orthogonal bivariate polynomials.