Game scripting engine

So I’m starting to get back into the groove of coding my game and I’m at somewhat of a roadblock on how much I should make scriptable.

So for a brain dump, I’ll state what am I looking for right now?

Dialog sequencing
Entity administration(adding/removing/altering)
Triggering other sequences
I’m wanting at least these features so at any given level I can do the following.

Tell a story as the level begins
Add stuff to kill
Do something if you die
Do something when the boss dies
Perhaps this is too much and should be hard coded in the game for a unique kind of boss mob. Not sure, but I feel that’s restrictive. I’ll start with the goal of these things now using some sort of xml scripting syntax.

I thought about using Lua or JS, but I just can’t imagine that it would be easier using that than some fixed rule system. So homegrown ScriptML it is.

Suggestions welcome!