Search your library for a Demon card, reveal it, put it into your hand, then shuffle.
Delirium — If there are four or more card types among cards in your graveyard, instead search your library for any card, put it into your hand, then shuffle.
Valgavoth whispered into Marina's ear until he was all she could hear.
In the case where Demonic Counsel's delirium ability allows you to search your library for any card, you won't have to reveal that card. (You could, but as your demonic counsel, I wouldn't advise it.)
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.