In this work we utilize ghost groups of Burnside groups introduced by Boltje and Danz in order to investigate fusion systems of finite groups, double Burnside modules, and biset functors. We give an expression for the coefficients of the characteristic idempotent associated to an arbitrary fusion system, and demonstrate that bideflation does not generally preserve this idempotent when the fusion system is unsaturated. Motivated by the theory of p-completed classifying spaces, we study when two groups are isomorphic in the left-free p-local biset category, and prove that two groups G and H are isomorphic in this category when there exists an isomorphism between their Frobenius p-fusion systems. Finally, we consider a process mirroring Green's theory of idempotent condensation and demonstrate that a generalized Burnside functor is the decondensation of the usual Burnside functor, and that this decondensation preserves the subfunctor lattice.