Question about Sidious in the Rebels finale

Any clue what type of ability he was using to access the world between worlds?

If he had more time could he have used that ability to force his way into the dimension alone? [he almost did as is]

Palpatine couldn't have physically accessed TWBW without a direct 'tether' to it... And that tether was Ezra.

That's why Palpatine never began physically entering the realm until one of the tendrils conjured by his Sorcery snagged Ezra's leg. That's also why Palpatine was instantly removed from TWBW when Ahsoka severed his connection to Ezra:
http://www.youtube.com/watch?v=WIieMZH4R8U&t=18m30s
*18:30-18:54

Just for next time, there's an "inquiries" thread, so if you want to ask any questions, you can use that.