Let's get this out of the way right now: Ong Bak 2: The Beginning really has nothing to do with Ong Bak aside from the fact that Tony Jaa is in it. Sure, you'll hear claims that he's playing the earlier incarnation of his character from the original, but that won't mean anything to you. Because you don't care about a plot. You came to see Tony Jaa fight a crocodile.
Actually, Tony Jaa doesn't get to fight a crocodile. His younger self does. That's the tip of the iceberg for what happens in this movie. Check this out, Ong Bak:
Is recruited to join a village where they'll teach him to be a badass. And magic, for some reason.
Runs on top of a herd of elephants only to school their punk asses with a slap on the head.
Ups the ante of the 30-dude arm breaking scene from The Protector (Tom Yum Gong) by attacking 30 dudes in the throat. He rips many out, and injures many more.
Pretty sure he fights a vampire. And not a pussy, Twilight-sparkly vampire either.
There's a ridiculous ending that just has an insane amount of people for Ong Bak to fight. And they keep coming, and he uses everything to fight them all. It might last a half hour long, this battle, and he uses an awesome nunchuck device, as well as an elephant, to defeat his enemies.
That's all you need to know about Ong Bak 2. The fight scenes are up to par with Jaa's standards, and do not disappoint. Story-wise... it's best just to ignore that aspect and pay attention to what you and every movie-goer wants to see: Tony Jaa kicking people with his knees.