It's an easy-to-cast commander that can just play anyone's lands and spells
Except for the listed exceptions, the tokens created by Grist, the Plague Swarm's last ability copy exactly what was printed on the original cards and nothing else
It cant bounce your own stuff, but thats usually more of a corner case than a primary use
Goblins, Dinosaurs, Ninjas, and Ne'er-do-wells, each pack has 1 of over 46 possible themes
Dont worry- Im not going to bombard you with a bunch of probabilities and calculations
Its maybe the worlds most complex game ever made (with almost 20.000 unique cards printed), but they managed to split their development and design to both very enfranchised players and new ones, making the game still interesting for long time fans and accessible to anyone who is trying to become a player