Whenever you cast an instant or sorcery spell, untap Unruly Catapult
That flexibility has seen the spell turned to all sorts of uses, from its natural home in classic Legacy Reanimator to one of the great meta-breaking decks in UB Deaths Shadow
If more than one player is instructed to mill at the same time (by the activated ability of Raul, Trouble Shooter, for example), as long as at least one nonland card is milled, Screeching Scorchbeast's last ability will trigger just once
Even today, she shows up in Premodern Reanimator decks
The best is Brainstorm since you draw three and then return two, so it's strong with putting back lands, expensive stuff, hiding from discard and reshuffling with fetch lands et all