Let's Try This One More Time

In the darkness, Kaspar checks himself before taking any dangerous leap off the side of the catwalk. He thinks to himself, "I didn't expect that to happen. So much for a flaming vat to scare off the warforged."

But the half-orc won't waste any more time with thought. Instead, he uses Castille's spear to launch a hard sneak attack against the warforged. Although the spear was set to intercept a charge attack, Kaspar uses his crouched position as the foundation for a quick thrust into any soft spot low on the thing's body. In fact, if he's successful, Kaspar will first attempt to push him backwards towards the gap, and second leave the spear lodged in his body -- thereafter drawing his rapier.

I know I don't have time for all of the above in one pass. I will usually write a bit extra just so you can get an idea of where I'm heading.

As for the attack, am I allowed to use my natural 20 for the attack? If so, then I come up with a 7+3=10 on the threat roll (can I use an action point here? If so, it comes up an extra 5 for a total of 15). Damage on the spear attack is 3+4+2=9 (two-handed attack). Also not as great as I was hoping for, but let me know if I scored the crit.