I got my new baby today. He is taking up residence in one of the bathrooms for the time being. I made the mistake of trying to intro the kitten to one of the other cats and my bengal Leo turned into the Tasmanian devil and I have some lovely scratches! Stupid me. Anyway, he was all freaked out so I got him back in the bathroom and calmed him down. I felt so bad. Anyway, how is the best way to introduce him to the other cats? Umm next time I think I shall not be holding him!

You should keep them behind doors for a week or 2 so they'll make aquaintance under the door, smelling each other .
You should also swap sleeping cushions in that time.

When they'll seem ok and try to play under the door, you can try putting them together

Depends on the cats - they may be ready before that. Don't rush them, but don't hold them back either.

Some cats you can just throw together in a room and they'll sort it out within a couple of hours. Depends a lot on the cats.