I could write a book on how intriguing this deck is, but I'll keep it simple:
Manaless dredge is a deck that runs zero lands-- or it runs 4 and they still call it manaless for some reason-- and it combos off fast-- only sometimes ever really combos off-- and has so few interactions that your opponent can't stop it-- unless they drop any of the like 6 graveyard hate cards that entirely shut down the deck.
However, we can now not just scoop on T1/2 when our opponents drop a Grafdigger's Cage or Rest in Peace.. Wow, how did anyone play Legacy Manaless Dredge before the printing of our savior Force of Vigor? Force of Vigor lets us pitch a green card, of which there are nine mainboard and even some are dredgers that are green, to destroy those nasty hate cards in game two.
Keepable hands are pretty easy too. Obviously it gets a little more intense game two as your opponent has assuredly boarded in some graveyard hate. The hope is to not have to mulligan ever, however.. that isn't always the case. Sometimes, a mulligan will put you further ahead than keeping a bad 7. Keeping at least one dredger is always nice. Street Wraith is a great card to have in your opening hand as well. Phantasmagorian is probably the best card to have in an opener. I could break down each card, but I'll just show an example of a pretty common opener for Manaless Dredge.