With a set covering a wide range of horror tropes, Delirium seems like a great mechanic to bring back to not only fit some of the horror themes, but to provide a fun, grindy mechanic to this set
Green doesnt have discard, but Disrupting Scepter does
If Golden-Tail Trainer's power changes after costs are locked in, or if Golden-Tail Trainer leaves the battlefield while you are activating mana abilities or paying those costs, the cost reduction effect won't be affected and the total cost to cast the spell won't change
More importantly, Scrooge McDuck, Richest Duck in the World has the ability I Didnt Get Rich by Being Stupid - which allows players to play an item for free whenever this card banishes another character on their turn
As such, the value of these cards is tied to an inalienable, irreproducible cultural significance rather than the relatively mercurial fortunes of a specific company