Assuming that he wants to accomplish the unthinkable by eating 3 devil fruits from 3 different categories, then he still needs a Zoan-type devil fruit. But not any Zoan-type, it has to be one of, if not the strongest Zoan there is. And it also has to compliment his other devil fruits somehow
I think Marco's Phoenix fruit is the perfect Zoan for him for a very specific reason, mainly is that it allows it's user to regenerate and heal the damage they take. Blackbeard suffers from a massive weakness inflicted upon him by his dark-dark no mi, which is the weakness of absorbing all the damage and attacks he takes. By acquiring the Mythical Zoan Phoenix devil fruit, he can easily compensate for that weakness by constantly regenerating and healing the damage he takes - which is far above what humans usually suffer from when they're hit by the same attacks
Will we see Blackbeard at the end of Wano? Could he maybe send someone to kidnapp Marco, or even arrive there himself to repeat the same process that he already done before with Whitebeard?
I think Marco's Phoenix fruit is the perfect Zoan for him for a very specific reason, mainly is that it allows it's user to regenerate and heal the damage they take. Blackbeard suffers from a massive weakness inflicted upon him by his dark-dark no mi, which is the weakness of absorbing all the damage and attacks he takes. By acquiring the Mythical Zoan Phoenix devil fruit, he can easily compensate for that weakness by constantly regenerating and healing the damage he takes - which is far above what humans usually suffer from when they're hit by the same attacks
Will we see Blackbeard at the end of Wano? Could he maybe send someone to kidnapp Marco, or even arrive there himself to repeat the same process that he already done before with Whitebeard?