I generally just hoard whatever I can get my hands on, not necessarily trading up specifically for them. But if I'm able to, I might. Mostly just casual hoarding.
The first thing I started hoarding when I joined in 2020 was any space themed pet. ^_^ I love them so much and they are pretty. I call it
The Final Frontier (mostly cause I found it funny..)
He's not currently In the hoard
(I have him in Dressed Up rn), but I kinda consider this little guy the mascot. ^_^
The second thing I started hoarding was
Christmas pets. :') I initially was going for just pretty ones, then just one of each.. now I've got almost all the pets from the advents put in there. (the ones that I own, that is) I sometimes do and sometimes don't put the regular December pets in depending on whether they give me Christmas vibes.
This one's also in Dressed Up atm, but one of my Christmas mascots. :3

I like both of these themes so much I tend to have a lot of the items related to these hoarded too so I can try and dress those pets up when i get the chance.
There's a few other small hoards I'm working on, but one I started a few months(?) ago was
Cafe. It initially started with just these coffee themed butterfly wolves.

And now has turned into whatever makes me think of a coffee shop. ^_^' Latte is the mascot for these guys.
(currently in Dressed Up)
Aizaka - so I can find my post later