These can be standalone scenarios (there are about a dozen available), or a series of these are linked together into campaigns or cycles, of which there are six so far
The transformation doesn't necessarily make the card more powerful, but it maintains Flash, adds Double Strike, meaning you double the damage output in combat, and shifts the card draw from opponents drawing two cards per turn to combat damage dealt to players
Curses give enchantment decks something aggressive and directional to add to the buff, stax, and value cards that populate these decks
Some sets are older and harder to find, and those cards are often more valuable
That's because Pokemon Sword & Shield (the video games, not the TCG expansion) changed the way fans experience the mainline games with its debut on the Nintendo Switch late last year