You're thinking too much in human terms. If it was left up to humans, then yeah, we need him to eat a tsar bomb and evacuate 1/6th the face of the earth.
What about monster terms though?
Seems like the headmaster's gonna bring it. What kind of monster is he anyway?
If Alucard is the first vampire, what's the first werewolf? Let's bring him in here.
What do you think the strongest monster is anyway?
Not the werewolf (he'd be the fastest)
The "strongest" is quite a broad term^^
If it is about physical strenght, then the stronest vampire (=true ancestor) would win, BUT if it came to pure potential combat abilities, I'd rather put the nine-tails on the place of number one^^
Why?
it is simple:
We saw the five- tailed fox youkai Kyou some time before Alucard awakened (he had only four tails in season 1, but he trained on a fifth one in the meantime and said that each time they get one more tail, their power doubles...
So simply put:
(I put "power into units of "1" which means the power of a 1- tailed spirit fox)
1 tail: 1
2 tails: 2
3 tails: 4
4 tails: 8
5 tails: 16
6 tails: 32
7 tails: 64
8 tails 128
9 tails: 256
That means that a 9-tails would be no less than 16 times stronger than Kyou of season two or 32 times stronger than he was in season 1, probably even stronger due to experience and knowledge
If 9- tails and Alucard were to fight all- out, Alucard would most likely lose
Kyou is at least 16 times weaker than the 9-tails and just his fire aura was hot enough to burn anything close to him (Tsukune won because he was so fast that he remained near him only for an instant)
Alucard is, as a vampire primarily specialized on melee combat, supplemented with some magic tricks
The 9-tails, when he/she is going all-out would produce a LOT of heat just by standing there and most likely use large- scaled fire-based attacks against that huge target
And here is the problem:
Cuts are quite easy to regenerate, but large- scaled burns that are repeatedly inflicted on Alucard WILL wear down his regenerative abilities as the destroyed tissue won't heal but has to be replaced...
Alucard can't evade into another dimension, at least not with that huge body and that is a teachnique developed by his archenemy and there are only a handful of people how can pull that off (especially the dodging technique)
Alucard (and his surroundings) would be burned to ashes and he'd never be able to regenerate from that
Moka's mom had that much trouble because she is primarily a melee type(like every other vampire as well) and wasn't good at large-scaled destruction due to her body size, giving her difficulty on suppressing Alucard
If Akasha and a 9-tails were to cooperate for that one, Alucard would be done for^^
Ah, I almost forgot:
What about water?
Are true ancestors immune against that?
If not, then just give Alucard a good shower and let Tsukune in shinso mode handle it (he is immune against water because he is a human)
And as we saw with Kokoa's sister, water also hinders all the super- strong techniques as well, so there is a good chance that he won't be able to do shit when confronted with water AND Tsukune in super- powerful mode