After taking a closer look: his middle toes should not show any feathers at all and taking into consideration his body type, his tail type and his rather big but too thin comb I suspect that somewhere in his ancestry there might have been added some other than pure Marans genes.
He seems to be still quite young, so could still be developing.
But @Chooks man already pointed to the main issues that will not disappear even as fully adult, i.e. the comb fork he is showing will reappear many generations later still and in itself would usually be disqualifying criteria and a...