Is there a figure in Buddhism corresponding to the Christian notion of such? And what would that mean, practically?
If you are using the word anti- as it is used in Physics then no there is no anti Buddha. In physics anti-proton or anti-electron are valid particles which when meet with their counter proton or electron they get annihilated i.e particle and its anti particle annihilate each other releasing energy. The particles die. But Buddha has no anti Buddha. Nothing can neutralize Buddha. Whether after death Buddha exists or does not exist is not known. However if you are using anti- for something or someone who opposes Buddha then yes there is Mara who opposes Buddha and everyone who chooses the path of enlightenment. Mara is not just anti-Buddha , he is anti-enlightenment.