A week or two ago, I ran across a player on Magic Online who cast a maindeck Lost Legacy. I scofed a bit to myself - the card does not seem very main-deckable, plus I didn't have many good targets even if they knew my decklist (and as you might guess, I was on a brew, and being early in the game, they didn't know what I was about almost at all).
They targeted themself.
And named.... Eternal Scourge
This combination is incredibly sweet. As long as the Scourges aren't in play or exile, you effectively "draw" four cards, since you get to cast the Scourges from Exile. Note that this isn't even messed up by drawing Scourges, since you get to "cycle" them in that case, putting them into exile (where you can still use them) and drawing a replacement card.
I am very intrigued by this combination, and set out to build a deck around it. Naturally you need the 4 Scourges, and if it's good, I think you want a pretty high number of Lost Legacy as well. The problem is that the remaining Lost Legacy in your deck are pretty bad. Of course, even if you draw two, you're still at a 3 mana draw three, which isn't the worst ever, but you do need to dock that Eternal Scourge isn't exactly the epitome of Constructed Power-level. Well, I could call it "Modern GP winning Eternal Scourge", maybe that would make me feel better. Point is, you want to be able to do something with excess copies, ideally. Fortunately, standard is full of discard themes, so it was just a matter of finding the right one(s).
Furthermore, the biggest weakness of Scourge is generally that it just trades in combat, and ok, that's fine, but it would be nice if we could do more. (Really the biggest weakness is that if there's a way to repeatably target it, you effectively can bounce it over and over - but fortunately there aren't too many of those in Standard). The card that really pops up as doing well in terms of interacting from the Graveyard is of course Scrapheap Scrounger, which with Eternal Scourge, not only returns itself, but gets you access to the 3/3 again as well.
This let to a couple additional directions. First, I wanted to use Vehicles. Lost Legacy for Scourge is a bit slow, Scrounger doesn't block, so you need to survive, and Vehicles let Scrounger let you do that. Plus all this stuff has three power, so it can be used for Crew 3 vehicles. Second, we go towards a Zombie shell. That lets us have discard outlets, which work well to get rid of excess Legacies, as well as playing pretty nicely with the Scroungers.
And that's the basic ideas of the deck. Let's look at the list:
I would have loved to have more Skysovereign, but it does cost 5, I think Pariah is generally a bit more important, and you can only have so many 5s in a deck with this kind of curve. Also note that if we can have more of these 23 lands be discard fodder, that's pretty desirable. Mindbenders are genearlly good, but also provide a nice way of getting stuff from play to the 'yard.
Amalgams are the only blue in the deck, but we are playing the full 8 duals. Maybe you can cut a few here, but they're not all that expensive to run (mana base is quite good), and if you think about what we have to get it in play, there's 8 discard outlets plus those 8 blue sources. Yeah, it looks like 12 discard outlets, but while Copter and Cryptbreaker work fine, Haunted Dead only gets you there if it's in the 'yard itself, which happens far more from having one of those other outlets in play at some point first, rather than naturally getting cast and then dying.
I'd like to make a few notes on the sideboard. First, Liliana as a one of here is kind of a joke - that card should almost certainly have a bigger role in the deck. Second, Shamble Back is probably even cheekier. When you have a scourge in the 'yard, it's a 1 mana 2/2 gain 2 draw a Trained Armodon - we're talking Legacy levels of efficiency there. When there's just some random creature, that rate is ok against aggro decks. Plus it's a bit of a mise on Graveyard hate.
In general, there are two ways you can lose - people go under and murder you too fast, or people go over the top. This is about the grindiest possible deck I can think of in the format, so I don't think going over the top in that sense is plausible, but it's possible of course to go taller, most notably with Emrakul. Marvel could be an issue. Fortunately enough, though, we have four main deck Lost Legacy that can help us with that issue. And we get access to a bit more help in the board.
Probably we should be a bit more concerned than we are with the aggro matchpus then - WRx is probably too fast for the way we're configured currently at least. I think we can hang with UW, but would be concerned that their cheap spells are simply more powerful than ours. Anyway, the deck is untested, but it's just the kind of mad scientist idea that I think really ought to be worth a test.