I'm liking it so far question though for the evolution I know people usually use a basilisk, but what about the gid of serpents the Norse god jourmangdr
You should let him not change in an human form he should stay a monster because the mc that return in human form ruin the stories and its a super cliché
I would like to see the reactions of the people coming in and they see the dead monster with the snake hanging on it before it gets scared and runs away from them