Multi-stability is important for sustainable design of multi-functional structures. Unlike many actuators, they don't need energy to be maintained in their functional states - but only to effect the transitions between them. Geometry can be used to amplify material responses, store and couple elastic energy to other stimuli. Magnetic structures are particularly interesting in assembly for these multiple advantages: - dipole moments from ferromagnetism can make permanent assemblies, but can also be reconfigured/disassembled - Interactions are much less affected by few environmental effects, as for example are electrostatics. Most everyday materials have the magnetic permittivity of vacuum, or close. We demonstrate assembly of magnetic Janus particles, which form stable structures in the absence of magnetic fields. Fields are used to disassemble such stable structures, and allow the possibility of recycling the building block particles. We also demonstrate the magnetic manipulation of macroscopic magnetic materials, including the first stable Pickering foams, which can be destroyed by magnetic fields. We also show challenges we've overcome in modelling simple structures such as spherical cap shells. High speed video of the cap flip driven by magnetic field, shows an asymmetric intermediate state before complete inversion. This has been modelled by finite element simulations to understand the energies involved in the transformation. By showing a number of phenomena, we hope to stimulate a discussion about the methods needed to improve simulation in magnetically driven actuation and assemblies.