Attack with The Wretched so you get their creature even if damage is prevented
of course, and be the only player at the table drawing off this
Some might prefer this to cantripping four-cost Dismiss since it's cheap and the card heads to your graveyard for delirium, reanimation, flashback and threshold purposes
A brief overview: Delirium was first printed in Shadows over Innistrad, where it was designed to mimic a society being driven mad by eldritch forces, culminating in the emergence of Emrakul on the plane of Innistrad
Generally, if you do manage to use it on turn one, youll get some use out of it even if your opponent does play Pokmon Ranger
The only means of getting rid of it is playing a card that'll wipe the board or prevent it from being summoned in the first place.