Basically press b2, immediately press down, wait until the first hit makes contact, then press and hold up. With a low poke, say d3, it would be d,3,u, and you can cancel that way. It took me a long time to get hang the hang of this, but once you do it's nice to know you can throw those in there every once in awhile just to mix things up.
As for his teleport inputs, I guess I'm just lucky. I played a ton of Zatanna in Injustice, so I was used to how the fingers have to move. That + using a hitbox = not ever a problem. People talk about how a hitbox doesn't help with MK the way it does other games, but I think Raiden is one of the characters that actually really benefits from it.