If MC originaly was a not a monster then you could have an arc where MC gets reminded of the time before. Ends up strugeling about his identity, wondering if he is a monster or not. If MC ends up on monster, make an arc at the end where MC goes on the offencive and ends up seeing his/her son/daughter with a child of their own (doing or having something to remind MC once more). MC wife/husband could also be there. This could then end with MC having to kill them, be killed by them or maybe die saving them and regaining his/her humanity? Should be the MC solidifying his position as a monster or doing a compleate reversal (those are the two choises i would have chosen from).
If MC is a monster from the start (no memories from previous life, or have never been anything else). This arc would also need some kind of arc before this one that woild explain why the MC would act and can act as he does there. It's as simple as MC drinks/eat something that transform him into a human (or another inteligent race) for an extended periode of time (weeks/months). Maybe there are two races at war (or two kingdoms where kingdom A mainly have race A nbd kingdom B, race B). And the thing MC devoured was made for infiltration purpose. So MC have to live with a new body. What would eventualy happen when meting race A, what about race B? MC later gets hold of that item once more, what would MC do?
You could also simply go for simple real life problems, like MC gets fleas. What problems does this bring? How is it solved? How does it affect daily life? When does MC find out something is wrong? How did MC get them? Do they bring the MC problems even after they are gone?
MC breakes multiple limbs.
How does MC deal with it? Is he able to live normaly? What chalanges does it bring? Hpw does MC survive with broken limbs? Will the limbs work normaly afterwards? Is the MC abandoned by the pack? If yes what happens if they meet once more? Do MC hold a grudge?
MC captured and sold to a circus. Does MC make a bond with anyone there? How is the MC released? Does the MC run away? What does the MC have to do there? Will the skills MC learn here be usefull later? Will someone watching MC preform , recognice him later? If yes, how does 5his affect how they act aroynd the MC? Does MC cause the end for the circus? How does this affect MCs relationship with others? This could end up in a later arc where MC is cought up in the aftermath of it's end?
MC could be pregnant or waiting for his mate to give birth. This couls happen at the same time as the arcs above. How does this change how the MC acts? How does the monster race MC is act while ecpecting children? Is MC diffrent from the norm of his race? How does his mate react to this?
MC runs away from someone or something (could be hin natural predetor or just someone much stronger), and ends up in a habitat compleatly different to what he is used to. Eks. MC naturaly lives in open plains but ends up ina swampy forest.
How does MC survive? Does MC get permanent damage? How does MC survive? Is it brains, brawn, luck or something else?
I should stop here. Just tell me if you want more
@FukinDeadBeat.
Would have writen something myselfe, but i just end up asking question after question to myselfe like i did here, just almost never ending...