We have studied the effect of the spatial distribution of B, N and C domains in 2-dimensional borocarbonitrides and its influence on carrier mobility, based on density functional theory coupled with the Boltzmann transport equation. Two extreme features of C-domains in BN-rich B_2.5CN_2.5, namely, BCN-I (random) and BCN-II (localized), have been found to exhibit an electron (hole) mobility of ∼10⁶ cm² V⁻¹ s⁻¹ (∼10⁴ cm² V⁻¹ s⁻¹) and ∼10³ cm² V⁻¹ s⁻¹ (∼10⁶ cm² V⁻¹ s⁻¹), respectively. We have ascertained the underlying microscopic mechanisms behind such an extraordinarily large carrier mobility and the reversal of conduction polarity. Finally, we have derived the principle underlying the maximization of mobility and for obtaining a particular (electron/hole) conduction polarity of this nanohybrid in any stoichiometric proportion.