Here are the main combos to stack your graveyard (to my knowledge):
Hermit Druid: you just have to build a deck with all nonbasic lands to be able to dump your whole library to your graveyard as soon as turn 3 (even turn 2 with some acceleration). This combo is so good that
Hermit Druid is banned in most formats.
Undercity Informer and/or
Balustrade Spy: to make this work, you have to build a deck with literally no lands. It's a tough task but not an impossible one, in fact it's the core of the All Spells deck.
Cephalid Illusionist +
Nomads en-Kor: it's an old combo that was the core of the Cephalid Breakfast deck. You can swap
Nomads en-Kor for many other cards (most notably,
Shuko) to get the same result.
Golgari Grave-Troll and other dredge cards: the engine desides the infamous
Ichorid deck (or lately dredge deck,
tout-court). There are many incarnations of this archetype to choose from, depending on the format etc.
Mesmeric Orb +
Basalt Monolith: I think this was first proposed for the Four Horsemen combo, but now it's used in many other decks (especially in EDH). You can swap
Basalt Monolith for many other cards.
Mirror-Mad Phantasm: this combo is mostly used in EDH. You play your only copy of the Phantasm, then you
clone it in some way and activate the
clone to again dump your whole library to your graveyard.
As a personal advice, beside
Morality Shift (which I don't think it's that hard to cast, after all), I would suggest
Necrologia: pay a bunch of life, keep
Songs of the Damned and
Consume Spirit and discard the rest,
boom!