Do forgive me for all these are from my play sessions on PSO2 JP, and I also have to apologize for the low resolution on some of these screenshots. Most of the time I didn't bother turning off the UI either. (I wish I had more to share, but sadly I lost so much stuff throughout the years.) If some are inappropriate, I'll delete them. It reminds me though, you guys could use a spoiler BBcode plugin or tags on this forum.
Encountered a Rappy in need of a health check.

Ever seen a Jason Voorhees Rappy?

I call it "Rappy Lost at Sea!"

Rappy Squad Only!

NSFW?

Hamburgers.

A wild Gengar appeared!

I knew Nyau's were bloodthirsty creatures, but to go after Lilipans!?

'Window Shopping' or Mannequins?

On the 'other' side of MyRoom.

When the game gives you 4 Emergency Codes simultaneously. (It's pretty rare, we got to appreciate the 'lagg' sometimes.)

A friend (Matt) made this screenshot some years ago, I couldn't remember saying 'that' to him during a Quna Concert.

The following aren't funny or creative but still are interesting.
It doesn't happen often, encountering Big Vardha in the Desert Area. It is fascinating each time.
I tend to encounter it once a year or 2. It's rather telling when you 'can' expect Big Vardha to make an appearance in Area 2. When your game session holds a Big Vardha spawn, you'll notice that the 'Exit/Entrance cliff' from Area 1 to 2 looks 'unique'. The cliff is situated a bit 'sideways' rather than it being perfectly in front of you. Not talking about the Exit/Entrance location on the map, but the rather unusual appearance of the Exit/Entrance cliff. Wish I had a screenshot of that, It's difficult to describe/imagine it.


The game has some spectacular views, a couple gems well hidden. Sadly, screenshots don't do them justice. (Especially 'Parallel Areas', the majority of them are quite gorgeous.)


The castle in Coast Exploration/Expedition, up close.

Sega could do a better job at cleaning though, don't sweep it under the rug. Halloween decorations/assets were found 'underneath' the lobby. Note, this screenshot was made long after the Halloween lobby expired.
These practices are actually quite common in the game industry. Instead of removing irrelevant elements and assets from the game, developers prefer to keep them around but move them somewhere (far away) hidden from the players.
Similar stuff happens at Bethesda within their Fallout games. I sadly forgot the name of the infamous room, filled with unused/testing components. There are more examples out there, but the Fallout one came to mind because it got hacked not too long ago.