Basically, when Orcish Bowmasters enters, or an opponent gets greedy when it comes to drawing cards, you get to deal one damage to something, and then also create an Army token or make that token stronger
"Wizards Is Releasing More Magic: The Gathering Sets Than Players Can Keep Up With"
The gist of it at current, however, is this: The Phyrexians have invaded Dominaria and have installed sleeper agents in every part of the plane, into every class and species in and out of society, and they've even turned some of the beloved legendary characters from the story into sleepers as well
Just having Necroduality in play means double the zombies, double the enter the battlefield triggers, double the fun
Since there's no better source than the actual emails, I'll be quoting them liberally throughout this article (in the cases where we need to reserve an idea for the future, the text will be replaced with bracketed italics summarizing it)