Simon Says "Doom" is an unfinished Invader Zimepisode. This episode never aired; only the script and a recording were made.
Zim volunteers to help out several children at the local orphanage as part of the city's "Bee a Good Neighbor" program, but Dib thinks that he is up to something, and volunteers as well so he can keep an eye on Zim. While the Irken is busy looking after a bunch of orphans, he begins to notice that children will do whatever he wants if he says "Simon Says" before his commands. Later, Dib, who is supposed to be monitoring the baby changing machine for any core meltdowns, checks up on Zim.
The orphans are rampaging the city due to Zim's "Plan B", so Dib operates a flying bee suit around the city, commanding each orphan, one by one, to never listen to Zim again. Once Dib goes back into the baby changer room, the changer is twenty seconds from a core meltdown. The meltdown is averted, thanks to Mr. Elliot, but the charger has to re-charge and Dib has to clean the baby filth by hand.
As it transpires, using the orphans to destroy the city was "Plan B", as Zim had never heard of "Simon Says" before this episode. It is unknown what Plan A was. Zim also tells Dib, after his plan is foiled, that his real plan was to distract Dib from the baby changer and cause a meltdown. However, after Mr. Elliot fixes that, Zim says that his plan was to make Dib clean the mess by hand, "all along".