Experimental observations of the low-lying states in 12Be and their accurate modeling play an essential role in understanding the disappearance of the N=8 magic number. Long-standing experimental ambiguities have been clarified using an one-neutron adding (d,p) reaction on 11Be using the ISOLDE Solenoidal Spectrometer at CERN’s HIE-ISOLDE facility. The single-particle energies of 1s1=2, 0d5=2, and 0p1=2 orbitals in 12Be have been determined from the extracted spectroscopic factors. A significant reduction between the separation of 1s1=2 and 0p1=2 orbitals is found in comparison with the carbon isotones, highlighting the breakdown of the N¼ 8 shell. These observations serve as an important test of different effects incorporated in theoretical models. It is found that two synergistic mechanisms, core deformation and weak binding, are responsible for the N¼ 8 shell breaking and the exotic near-threshold phenomena observed in 12Be, including the narrow unnatural-parity resonance 0−1 and the possible halolike nature of the 0+2 isomer.