H Scene 18 - Go to the sea god place in the first city. Go down the right staircase and talk to the person. Sakura should offer to go in your place.
H Scene 20 and Monster 173 - Lose and win to the Spirit World Beast, which is the boss of the sea cult sidequest. To do it, go to the sea cult (yes, the same as above) go into the right staircase and enter yourself. Then go to the southeastern door (someone was blocking it when you got here the first time) there will be a lot of horror movie shit on the room, but after you examine everything and try to leave, a pot will break, examine it to get a candle.
Then leave and go down the left staircase instead, going through the same route you went to save Conlon (the futanari girl), when you reach the final room, there will be a hole you can go through to get to a strange post-apocalyptic modern world setting. Explore it to find the boss. Also, enemies 41-44 are normal encounters here.
Number 17 is a normal enemy encounter that can be found at Dragon's Peak.
Number 128 is the last of the Golden Enemies. You can find him in a particularly conspicuous room in the underwater place, it's just that he doesn't show up everytime. From the beginning, go directly up and then through the northeastern path, that's the place.
Numbers 191-196 are all the various forms of the post-game boss, Star Child. Yes, she is the final challenge, but you can still keep going after beating her. As a side note, when she goes Blade Form, she gets a ridiculous amount of HP and Defense, but don't be fooled, you only have to whittle down a tiny portion of her HP bar for her to change forms again.