It introduces special guests, which are highly desired reprints that match to the world and flavor of the world they appear in
Im pulling Norns Annex for it
Then, for each Tamer you have in play, delete 1 of your opponent's level 4 or lower Digimon
During the Deck the Halls sale last month, I put together a Legendary deck, take a look here if you want to check it out
So, if you have a card with Prowl in your hand but something like Conspiracy has changed it into a Spirit, you must have done combat damage with a Spirit card in order to cast it for its Prowl cost
It also comes with the added benefit of putting a +1/+1 counter on it each time one of your creatures enters the battlefield so that you can put a bit of extra pressure on your opponents