This is exactly what happened to Lugia VSTAR a couple of months ago, that remained viable by swapping the colorless attackers with Single Strike ones
You can also expect more Trainer Full Arts, Illustration Rares, Special Illustrations, Immersive Cards, and Crown Rare Cards when the Expansion is released
I think for at least some of the people who bid for these expensive cards, it's more about regaining a lost part of their childhood than it is about snagging a card they can hopefully sell in a few years for a profit
The other notable one is Hostile Hostel, which can transform into Creeping Inn, a 3/7 horror construct that exiles a creature card from a graveyard when it attacks, before each opponent loses X life and you gain X life, with X being the number of creatures it has exiled
I always use the Dueling Nexus deck editor to build my decks I always use the shuffle button to test my opening hands before I test the deck in a duel