Missable items. (Contains some spoilers).

[Smasher]

A few notes on the missable things in the game, some spoilers are included.




Photos: Make sure to scan and photograph every boss and mini boss, as you will not get another chance, unless you replay new game plus.
Other missable photo subjects are the penguin in across, as he will disappear after completing the side quest to repair the elevator, the alien smoking hookah next to your apartment in neo, as he will disappear after fighting the queen for the first time.

Steals and summons: make sure to use steal on every boss and mini boss after getting Rosie, and Pablo. It’s not tied to any achievement, but they have useful items.
You can also capture a lot of bosses and mini bosses to use as summons, if you don’t see a “no capture” icon on the top left of the screen it means you can capture it.

Paws weekly and the maiden voyage side quest outcome: When you are asked to find clues during the side quest, go the room next to your sleeping quarters, and examine the bag on the bed to get the magazine (and the missable achievement). Return to the control room, and examine the vent hole in the far right end of the room to get the clue. Finally show the “Paws weekly” clue to the giant cat, and show the vent clue to the axolotl-like alien. This ensures both of them survive at the end, and each give you great artifacts as rewards.

[Shenai]

While the thing about Jules is true, there is an optional sidequest boss late in the game of the same species who you can scan in battle. So if you missed Jules but only realized too late, you don't have to reload an older save.

It's on Neo, if you come back later and walk right from your appartment you will run into a scene there that starts a quest. Where your hookah smoking alien neighbour lives. Who will have disappeared by this time. I don't think I've seen another one of his species anywhere.

[Smasher]

Thank you for the information, I didn’t notice because the boss’s health was already visible so I didn’t bother photographing him. I will remove Jules from the list.