Gameplay-wise, Altered features two combat lanes (called Expeditions), each led by a Hero, and uses a flexible resource system where cards can be used as energy, kind of like what you see in Lorcana or Pokmon
Do they sell now while prices are absolutely nuts and hedge against a potential Reserved List repeal that would cost them thousands of dollars, or do they hold on knowing that the same argument for selling could have applied in 2015, and 2013, and 2010
For decks where you need to find specific cards to set up quickly, Lucky Helmet is an immensely helpful Tool to have on hand
If you want to delete a Pokemon, just click on the image and poof, it'll disappear
Articuno ex, on the other hand, requires three Energy to dish out 80 damage, but they will simultaneously deal 10 damage to all of your opponents benched Pokemon