Bone Tower customs

Erection of the Bone Towers:
Spell
Add one Bone Tower monster to your hand. While this card is in your graveyard, your monsters can not be targeted by card effects if your opponent can not target them for attacks.

Soul-Crushing Bone Tower:
Level 3 Dark/Zombie, 400 ATK/1000 DEF
"If you control another Zombie-Type monster, your opponent cannot target this card for attacks. When a zombie monster is sent to the graveyard, send one card from the top of your opponent's deck to the graveyard for each zombie monster sent to the graveyard. Once per turn: If the only face-up monsters you control are zombie-type monsters, you can special summon a Zombie-type monster from your hand with 400 ATK.

Overlord Zortan, Dark Master of the Bone Towers
Level 12 Dark/Zombie, 1600 ATK/4800 DEF
"This monster can not be normal summoned or set. This monster can only be special summoned, from your hand or banish zone, if you control four 'bone tower' monsters. If you control another Zombie-Type monster, your opponent cannot target this card for attacks, and Zombie-type monsters you control are not affected by your opponent's card effects. When a zombie-type monster is sent to the graveyard, send the top three cards of your opponent's deck to the graveyard, and negate the effects of any cards sent to the graveyard by the effect of a 'Bone Tower' monster.