MotM describes amohaji as small aquatic dragons, dwelling in sewers and catacombs. They have natural camouflage and a mischievous demeanor. Their powers include breathing fire, telepathic powers, charm and compulsion effects, (un)locking doors remotely, shapeshifting, and magic armor.
M&B describes amohaji as small cousins to cloud dragons, masters of illusion and mental manipulation, breathing steam and forgetfulness, and living in migrating cloud lairs. If you kill them, then you can dig a magic pearl out of their skull that lets you cast some of their magic for the next 24 hours until it dissipates.
The two couldn’t be more different. However, the backstory of MotM states the amohaji migrated to the underworld after humans hunted them down ages ago. Perhaps those presented in M&B represent the amohaji before they migrated and adapted to the underworld.