This means that abilities that trigger whenever a creature attacks wont trigger when it enters the battlefield attacking
In fact, most decks rely on sending cards to the graveyard including but not limited to Dragon Link, Virtual World, Eldich, and so on
These in turn could be exchanged for prizes, the top one of course being the coveted Holographic Master Scroll card
Based on the name and some other info, it appears the theme will be alternative Digimon (subspecies, alternate evolutions, that sort of thing.) Some additional info suggests Omegamon Alter-S and ShineGreymon will have a focus, but it isn't clear at the moment if that's solid info, or just solid guessing based on what else is coming out the same day (more info on that below), although both make sense based on the theme and that they haven't gotten cards in awhile
How about adding them to a Commander deck