Having been to lembeh in both May and dec I have ticked off a lot of the critters but man I would love to see a hairy octo, maybe one day! Also the rhinopias but probably better luck heading to Ambon or Bali. Seems to be a lot in Padang bai area given peoples posts.
I think sept u will find blue rings though I think peak is dec-jan for mating. I went in dec and saw one then 2 weeks later people saw them on every dive. Rhinopias are few and far between in lembeh, small paddle flaps in deeper waters are sometimes seen. Mimics and wonderpus always a good shot to see one of them if not both.
Again Froggies year round but they do cycle like everything else. In both may and dec seen hairy, shaggy, painted, warty, giant, and in May sargassum and hispid.
Shrimps I think are all year but u need a good guide who is interested in them. Little green shrimp, hairy and algal shrimps they will find if u ask. Saron shrimp I spent 2 dives getting photos of one - highly recommend pintu kolada site in the rubble pile where mandarins are to find them. Bumblebee shrimps at madadir in the black sponges, harlequins they had both times at Serena.
Pipefish seems to cycle to most for me. Have never seen loads of ornates, more robusts, odd delicate and rough snout but still waiting in halimeda and velvets and hairy ghosts.
At the end of the day the guides will have a good idea what is around as everything cycles and the cycles move. Write a list like I did (60 critters mine was lol) and get ticking.