the whole image is one massive inside joke

/trash/ is a pseudo-board that exists on 4chan
whenever a thread is deemed off-topic for the theme of a board, the mods send it to /trash/

Now, 4chan does not have a dedicated furry board, and the core userbase of 4chan is VERY anti-furry, meaning that anything furry related gets sent into /trash/.

MLP does have it's own board, but only SFW threads can be posted on /mlp/
This means that many users will actually start MLP porn thread directly on /trash/
Similarly, many users will rather start furry related threads right on /trash/ to avoid problems with the mods.
These factors have lead to /trash/ becoming 4chan's unofficial furry board.

Also, some mods simply abuse their power, and just send anything they dislike to /trash/ which is why Steven Universe and The Loud House are there (some people think that all Loud House fans are incest fetishist).

The possum is the board's gijinka, /trash/-tan
she is a possum, because those rummage through trash, and she is anthropomorphic because of furries
and she is fat because "all furies are sick degenerates"