Does the following answer your queries?
WHO THE HELL THOUGHT IT WAS A GOOD IDEA TO MAKE REBORN TENGU? SERIOUSLY. I KNOW WHOSE FAULT IT IS. IT'S DEFINITELY VRAI'S FAULT, BECAUSE EVERYTHING IS FRICKING VRAI'S FAULT. HE WANTED TO TROLL THE YUGIOH TCG SO HE E-MAILED KONAMI WITH HIS REBORN TENGU CARD DESIGN AND KONAMI BEING THE BUNCH OF DUMBASS TOOLS THAT THEY ARE, IMPLEMENTED THE DESIGN INTO THE GAME. Reborn Tengu is like a ****. Just keeps coming back for more. Honestly, it doesn't matter if you kill it in battle, with a card effect, or even removing it from play. It doesn't matter if the opponent uses it as synchro or XYZ material either. THEY STILL GET ANOTHER TENGU FROM THE DECK. There are only two ways to stop Tengu from using his ability. You either flip the bastard face down with your ONE copy of Book of Moon or you spin the card back into the deck. ANY OTHER METHOD WILL JUST RESULT IN THE OPPONENT GETTING ANOTHER TENGU FROM THEIR DECK. There are plenty of cards in YGO which can replace themselves one way or another. There are two things which set reborn tengu apart from most of these other cards. Reborn Tengu is far more flexible in replacing itself and he has 1700 attack. Most other cards have a far more situational replacement condition and have far less attack. "But with three copies in the deck, at maximum they can only use his effect twice right?" Yes, very perceptive. Under ordinary circumstances you are correct. HOWEVER. There is a card called Pot of Avarice which basically allows the player to shuffle 5 monsters in the graveyard back to the deck and draw twice. So once the reborn tengu duelist is on their final tengu, they can shuffle the other two back with Avarice, making the third tengu active again. IN THEORY, THEY CAN USE TENGU'S EFFECT AROUND SIX TIMES IF THEY RUN THE STANDARD DOUBLE AVARICE. So to summarize, Tengu is a busted piece of crap because of his high utility to replace itself and very decent attack score for a 'floater'.