[Goofy]

I believe Tobi is obito as well. The similar sounding name.

The fact that the eye that Tobi gave to kakashi is covered by a mask on tobi.

The fact that tobi's body is crushed and obito is wearing a suit with stuff that looks like nails and rivets in them (before he became an akatsuki and got the cloud robe you could see his body suit)

Maybe madara took tobi's body but tobi's soul comes up once in awhile resulting in split personalities of tobi (childish and serious).

Also, as said above, madara's magekyo sharingan looked different after he took his brother's. The pattern was combined.

Everyone's magekyo looks different. Kakashi/itachi/madara/madabro all had different looking MS.