  We use the complex $\phi^4$ field at finite density as a model system for
developing further techniques based on worldline formulations of lattice field
theories. More specifically we: 1) Discuss new variants of the worm algorithm
for updating the $\phi^4$ theory and related systems with site weights. 2)
Explore the possibility of canonical simulations in the worldline formulation.
3) Study the connection of 2-particle condensation at low temperature to
scattering parameters of the theory.
