56mm x 87mm card sleeves Standard USA (56x87mm) and Fluxx Standard USA Game Size Sleeves

I got this and just regular binders, not sure of what Id settle on

For rebacked cards you can usually use the bend test (which will usually cause the two pieces to separate a bit near the crease)

The D23 promo version of Maleficent, Monstrous Dragon, and every other promo from the event are likely to maintain their value over time, making them solid investments if you happen to have a few in your collection.

Notably, Heikala, the artist for this card, was supposed to get their own Secret Lair

The English version's name is 'Hallo-Ween!', not the Japanese version's 'Trick or Treat!', and is similar to this in other TCG language versions