Unizombie
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You can target 1 monster on the field; discard 1 card, and if you do, increase its Level by 1. You can target 1 monster on the field; send 1 Zombie-Type monster from your Deck to the Graveyard, and if you do, increase its Level by 1, also you cannot attack for the rest of this turn, except with Zombie-Type monsters. You can only use each effect of "Unizombie" once per turn.
1)Unizombie let you to incrase 1 level of a monster by discarding one card.So it work with Immortal zombie deck,cuz in the field Unizombie, Zombie world and another monster,incrase the level of the other monster by sending 1 Immortal monster from your hand.Then you activate Book of life to bring back that Immortal(It is zombie due to Zombie world).
2)Unizombie let you to incrase 1 level of a monster by sending 1 zombie type monster from you deck to your grave.And once again it works with Immortal zombie deck,cuz,Zombie world,Unizombie and another monster in the field.In the grave you send Mezuki to incrase the level of the other monster.Then you banish Mezuki from the grave and summon the Immortal monster from the grave.(It is zombie due to Zombie world)
In both cases if the other monster is level 2,you make it level 3 and then build the overlay,and summon a good rank 3 xyz monster.