Responses
gios second persona is argio (aka cruel beast)
he was punished to the black forest bc he grew horns and there was some tradition to do that (he turns out to be a saint and a dragon aka a gods child)
the deer is a being from that forest and i think is implying his deer friend from his days as argio since he was intelligent and somehow taught a deer how to speak

Someone PLEASE spoil me on what the deer at the end is referencing or implying (๑•ㅂ•)و✧