Rather than use discard people would historically use self mill so that not only would the Ghoul be in the yard but also 20+ power of dorks, perhaps some guaranteed way to recur is involving flashback cards and Narcomoeba
But if you can second-guess their priorities from that first choice, you can try and follow up in a way which disrupts them
Still, when you look at a set like Edge of Eternities , there are only fifteen Legendary Creatures, with a good amount of those being the same character at different points in the story
If you're playing Hearthstone and know that the new meta is dominated by gurgling Murlocs, you'd normally have no option but to buy a dozen random packs and hope you draw what you need, putting a quite a lot of money into ActiBlizz's pocket along the way (and even then you're not guaranteed that you'll get the cards you want, potentially prompting further purchases)
In that time, many cards have entered the format, but not a lot has changed
Opposition Agent is a nuisance to play against