If there are 3 "Towers" on your field, suicide "Pyramid Turtle" to Special Summon another "Pyramid Turtle" and repeat the process as many times as possible. This can send 18 cards from your opponent's deck to the graveyard.
Once on the last "Pyramid Turtle", Special Summon "Goblin Zombie" and suicide it to bring a "Kasha" into your hand. Special Summon "Kasha". This will cause a chain in which the "Soul-Absorbing Bone Tower" will activate first, and "Kasha" will be last. When resolving, it will return all other monsters on the field to the decks, then sending 2 cards from the opponent's deck to the grave for each "Soul-Absorbing Bone Tower" in the chain. If done correctly, this will deplete any monster presence of the opponent's on the field, leaving you with a 3000 minimum Attack monster, in addition to the satisfaction of seeing those same monsters being sent into the graveyard.
Also, you can suicide "Vampire's Curse" into an opponent's monster with more than 2500 ATK and keep activating its effect to activate the Towers' effects.
While you have "Zombie World" face-up, use "Giant Rat" to start off the chain, ensuring you can summon up to 6 monsters with this effect (2 more "Rats", 3 "Turtles", and one "Zombie" that can be searched by "Turtle"), and milling 36 cards from your opponent's deck, which can form an OTK if your opponent started with a 40 card deck (he/she will have drawn 5 cards for his/her starting hand, plus a 6th card for his/her first turn).
While you have "Zombie World" face-up, if you have "Gilasaurus" in your hand, you can Special Summon it to send more opponent's cards to the graveyard. In addition, if your opponent chooses to Special Summon a monster from their graveyard, you can discard a grand total of 12 cards to your opponent's Graveyard per copy of "Gilasaurus".
When trying to mill your opponent's deck with 3 of these cards, your will probably run out of empty Monster Card Zones to Special Summon. A nice combo is to use "Il Blud" to Special Summon "Spirit Reaper". Since "Spirit Reaper" is being targeted by "Il Blud", it will be destroyed once it reaches the field, and you will have an empty zone to Special Summon it again next turn. Another combo to use is "Il Blud" and "Bone Crusher". Since "Bone Crusher" is being revived by a Zombie effect, it will destroy itself during the End Phase. With 3 of these cards on the field, simply revive "Bone Crusher" every turn, while also destroying one spell or trap card a turn.
Use any number of copies of this card with "DNA Surgery", "Colossal Fighter" and either "Lava Golem" or "Grinder Golem". "Colossal Fighter" can continuously attack "Lava Golem" and revive, while "DNA Surgery" will turn him into a Zombie once on the field, thus triggering "Soul Absorbing Bone Tower's" effect. Note that this does not work with "Zombie World", as "Colossal Fighter" would be treated as a Zombie-type monster in the graveyard, and thus cannot revive itself.
This card is perfect for "Malevolent Mech - Goku En", as Goku En is sent to the Graveyard if it is the only Zombie on the field when summoned by its effect and this card cannot be targeted if there is another Zombie on the field.
Combine this card with Zombie World, Dark World Grimoire and play The Wicked Worm Beast with a hand of at least 7. Worm Beast will go to your hand at End Phase and will go over your hand size limit. Discard Worm Beast and use Grimoires effect to Special Summon him. This creates a never ending loop which will mill your opponents entire deck in one turn.
This card can be combined with the effects of "Imperial Iron Wall", "Card of Safe Return" and "Plaguespreader Zombie" to have "Soul-Absorbing Bone Tower's" discard effect activate in an endless cycle that will allow you to win by having your opponent deck out during your his/her next draw phase.