Theyre a simple, fair source of card advantage, and this set is chock-full of things that make Clues
Soulstone Sanctuary, while Mutavault by no means, pairs nicely with Unholy Annex and as a new creature land Mono-Black can carry
While there were several competing styles of Survival decks around the time of its banning, the one that really ignited the controversy was Calebs Vengevine/Survival deck that would quickly put all its Vengevines into the graveyard, then play a couple of Basking Rootwallas for free, leading to extremely backbreaking assaults (frequently in the air, thanks to Wonder) that were immune to most forms of interaction
Then theres also non-signed cards, such as a Near Mint Beta Chaos Orb
It doesn't seem to be available to everyone, and we're not sure what the criteria are, but it's worth a shot