dont work, since DNA Surgery (called zombie) is active, u dont have a beast/beast warrior/winged beast to discard for Mantacore's effect

DNA Surgery only works on the field, not the hand. So he can do this combo as many times as he has Beast/Beastwarrior/Wingedbeasts in his hand.

Afterwards, he won't be able to keep tributing since he'll have nothing left in his hand and the field is nothing but zombie's.

Ok. This wouldn't work for one of two reasons. First of all, Read Mantacore's effect. It says that you need to discard a Beast/Winged Beast/Beast Warrior from your hand or the field to bring back Manticore when it was destroyed in THAT turn. (( You don't know how many people miss this little fact... ))

So. Let's put up this little scene. I'm assuming that you're going to run a Zombie deck, so here goes.

First, you play a card, in face up attack, or face down defense, doesn't matter. Then you set DNA surgery. You end turn.

Your opponent makes his move, throwing down a Archfiend Soldier, attacking your card. Let's just say that it was Spirit Reaper, so it doesn't die.

Your turn again. You play Soul-Absorbing Bone Tower, then end.

Their turn again. Gonna let you figure out this one.

Your turn again. You play DNA surgery, changing everything to Zombie. You sac Reaper for Manticore, and play Manticore onto the field. Tower's effect triggers, and your opponent grumbles. You attack and kill his soldier.

Now, here's the tricky part. Your opponent could do a number of things. Play Heavy Storm, MST, Breaker, Dust Tornado, Jinzo, etc, taking out DNA surgery so everything goes back to normal. But, on the other hand, he could also play something to kill your Manticore, and if all you have is Zombies, then you wouldn't be able to bring him back at the end of the turn.

Although it's a good stratagy, your best bet is to just stick to the Reaper and Tower thing, since that would leave you with a wall of sorts.