Methylammonium lead iodide (MAPI) is one the most promising materials for photovoltaics. Notwithstanding the above, access to its phase diagram and the underlying structural & dynamical properties has not been a trivial task. Building upon our recent study on TOSCA [J Phys Chem Lett 7 (2016) 4701], this proposal seeks to extend this work along the pressure axis using OSIRIS, in order to probe the onset and underlying nature of stochastic motions of the organic cation. Given the soft nature of the material, phase transitions occur at relatively low pressures ca. 0.3-0.4 GPa, yet their precise nature remains a matter of debate. In combination with synchronous diffraction on OSIRIS and computational modelling, neutron data over this pressure range and across the phase transition associated with cation ordering would pave the way for a detailed atomistic model of the material.