facio

Facio, facere, feci, factum is a third conjugation verb of the -io type, and it is irregular in exactly the places you use most. Its imperative drops the ending to a bare fac, one of the famous four alongside dic, duc and fer. Its passive is supplied by a separate verb altogether, fio, fieri, factus sum, to be made or to become, which is why this cannot be done comes out as hoc fieri non potest. In compounds the a weakens to i, giving conficio, perficio and efficio, and the supine factum gives fact, factory and, through French faire, a great deal else.