What is Tobi's weakness?

Answer 1

if you mean "like" as in a romantic sence i dont think he likes anyone in that way, but if you mean "like" as in get along with; i would have to say his team-mates and anyone who doesnt oppose him

Answer 2

Kakashi's sharingan is one weakness, since it was Tobi's originally, it shares certain properties with its counterpart eye. Namely, the place Kakashi's 'kamui' takes things to, is the same place Tobi goes to or takes other things to, using his Space-Time Migration jutsu.

Kakashi noticed that after Tobi became intangible to avoid Naruto's attack, his mask was damaged. He realised it was due to a lightning enhanced kunai that he had transported away using kamui. He was able to prove the relationship between the two techniques by warping a Rasengan away, causing damage to Tobi's arm.

Kakashi explained that when Tobi became intangible, he was warping parts of his body to another world, of sorts. Anything in that other world, is able to strike him. Tobi said understanding his jutsu wouldn't help them defeat him. However he fell for a ploy where a rasengan-using shadow clone was warped away by kamui, when Tobi thought it had been destroyed. Naruto used the tailed-beast ball attack on him, and Tobi warped out to avoid it. However while he was in the other world, the clone attacked him. Without being able to warp back due to the tailed beast ball occupying that space, Tobi could do nothing as the clone struck him in the face, shattering his mask to pieces.

Answer 3

He is actually Uchiah Madara, the strongest Uchiah, and in one episode defeats the three tails with a single jutsu, he also possesses the ability to make things pass through him. He has the mangekyou sharingan with unlimited use, and can control the nine tails beast, hence the beasts mention of him to sasuke. He is easily even stronger than pein, and it is unlikely that anyone can beat him. except naruto of course.

So, in short, he has epic strength.