I have 6 sources of heavy drawing:
Return of the Wildspeaker,
Rishkar's Expertise,
Garruk, Primal Hunter,
Momentous Fall,
Life's Legacy, and
Greater Good. Statistically, I am bound to come across either of these cards every 16.5 cards. As long as I cast one with
Mr. Multani in play (or another beast), using one of these drawing engines will get me at least one of the other ones, creating an exponential situation (even if I don't fish for any of the above-mentioned cards on my 1st draw, I am also quite likely to come across
Regrowth or
Eternal Witness to re-cast the spell). This is how this deck takes off - and the more opponents, the bigger and crazier the draws, to the point that I have to be careful of not milling myself. For this reason, I want to have as much mana as possible to fill my board with stuff every turn, drawing often to maintain a high tempo.
I have 3 permanent tools to ensure I get the best draws: Sensei's Divining Top, Sylvan Library, and Mirri's Guile. These will not only be on the lookout for land and mana but also raise the chances of fishing up a trampling or a drawing source. To further help get out of a "topdeck lock" I have 22 sources of library shuffle in the list.
Sorceries: Rishkar's Expertise - delicious on Multani, Maro-Sorcerer. Life's Legacy: less ideal but a no-brainer, as drawing multiple cards for 2 mana is most often better than having Multani in play.
Artefacts: Sensei's Divining Top is here mainly for 2 reasons: to ensure I drop lands every turn, and to filter through the deck in search of any of my 6 drawing spells (there are 21 shuffling sources to make the most out of it). The top can also provide a crucial extra draw. Staff of Domination is like a swiss-army knife that adapts to many situations (though its presence is mainly to enable a game-finisher infinite mana/draw/gain life combo). If I have a lot of spare mana and no way to go infinite, I will use the staff to draw at the very least. The Great Henge compensates from the pain of Sylvan Library, the Fetchlands, and Ancient Tomb, while allowing me to cantrip every time I drop a creature (even if I don't cast it from my hand, which is extra sweet with Chord of Calling, Natural Order, Crop Rotation (for Dryad Arbor), Green Sun's Zenith, Finale of Devastation, and Genesis Wave. Finally, Thought Vessel will give me ramp while allowing me to keep all those cards I'll be drawing with the big drawing spells. Skullclamp helps when I'm ramped up but out of gas. There're a ton of dorks to sacrifice for the greater cause. Also, it helps opponents think twice before blowing up creatures such as Selvala, Heart of the Wilds or Kamahl, Fist of Krosa, etc., or to get 2 cards after someone wipes the board for a quicker recovery.
Enchantments: Sylvan Library will help tremendously to fix/extra draw. Survival of the Fittest will convert any creature in my hand for a better option. Greater Good = instant sac outlet for drawing "in response to" or during Combat Phase. I always save Concordant Crossroads to surprise opponents with a monstrous hasty Multani to go for the kill, for putting down a Selvala, Heart of the Wilds, Karametra's Acolyte, or Priest of Titania that suddenly tap for absurd mana (or to go infinite if I have Staff of Domination). I play Garruk's Uprising the turn after I cast Multani (just as I do with The Great Henge). With Hexproof, the main reason why he'll end up in the Commander Zone is after I sacrifice him. So this last enchantment is almost always a cantrip, allowing Multani to gain a surprise trample and take 1 opponent right away (this enchantment also triggers with Kogla, the Titan Ape, Craterhoof Behemoth, Kamahl, Fist of Krosa, and Nylea, God of the Hunt - as long as I have enough devotion). Mirri's Guile helps out if I run out of gas and I'm relying on topdecking. She provides consistency, allows me to keep risky hands, balances the trade-off when I mull a few times, irons out the draws when the deck is not delivering, etc.
Creatures: Craterhoof Behemoth gives creatures Trample - Kamahl, Fist of Krosa does so too while being able to react against Wrath-like effects or creating multiple Overrun effects (I lost count of how many games I won with him!); Eternal Witness for strategic recoveries (usually to re-cast a drawing spell or recover a destroyed trampling source); Nissa, Vastwood Seer
(when flipped) gives me 1 card "draw" per turn or beasts; Scavenging Ooze is amazing against graveyard shenanigans (plus gaining life is always welcomed); Selvala, Heart of the Wilds's triggered ability will always trigger when I cast Multani so I get an extra draw; Quirion Ranger can do sick things by untapping Selvala, Heart of the Wilds or Priest of Titania and will also compensate if I miss a land drop early on the game.
Planeswalkers: Garruk Wildspeaker will give Trample to all my creatures if not dealt with within a turn, while also being able to generate beasts or untap lands for ramp. Garruk, Primal Hunter will generally do its -3 as soon as it hits the field if Multani, Maro-Sorcerer is in play with a hefty power/toughness, and can also generate beasts to block/attack with and potentially draw us 3 cards next turn if I'm desperate.
Instants: Return of the Wildspeaker is a great dual-purpose card that can target Multani, Maro-Sorcerer for draws or pump my creatures for a killer attack.
Lands: Reliquary Tower is great for keeping all the cards I’ll be drawing. Dryad Arbor is tremendously practical in a myriad of ways; the best thing is that it is easily fetchable being a Forest. Strip Mine deals with key utility lands, or for a strategic crippling of mana (especially against multicolour decks), and can be fetched with 2 different cards. Deserted Temple is here to untap Gaea's Cradle or Nyxthos, Shrine to Nyx, Ancient Tomb (if I really need that extra mana!), or even a forest if I have any of the doublers out. I've limited my non-basic forests in order to maximise Vernal Bloom's effect and minimize effects from cards such as Back to Basics, Blood Moon, etc.
Life gain: The Great Henge, Scavenging Ooze, and Momentous Fall are the only ways for me to gain life. These are added bonuses which help compensate for aggressive Sylvan Library Turns, a hot Mana Crypt, an early Mana Vault or Ancient Tomb.
