Explaining to someone why Plants would even be fighting Zombies is hard enough on its own. Try to figure out how to teach someone to actually play the game.
Princess Boo, playing as Rose, sort of teaches Mom how to control Kernel Corn as they take on hoards and hoards of Zombies, from Soldier Zombies to Plumber Zombies to Superhero Zombies.
Do they defend their flag with honor and leafy justice? Do the Zombies overwhelm them and raise their own stinky flag?