Board Thread:Questions and Answers/@comment-26456251-20160903194500/@comment-27701762-20160903214025

That line of dialogue (if I'm properly understanding what you're saying) occurs when you spare Asgore for a second time (or it might just occur the second time around if you also spare Asgore, or something along those lines; regardless, it's after you beat him the first time). He kills himself to give you his soul (which Flowey then destroys).

I'll try to answer the questions in order:

1) As I said above, Asgore kills himself.

2) Not unless you do a True Reset. Flowey refuses to fight you because he knows what will happen (i.e. the souls will rebel).

3) Asgore at first decides to take care of the protagonist, but then changes his mind and decides to give them his soul so that the protagonist can return to the Surface and find some other way to free the monsters (without needing to continue the war or kill more humans). Why does he change his mind? I'm not entirely sure.

4) Your TP route isn't ruined. The only kills that matter are those which give you EXP and increase your LV. And any such kills that are undone by reloading a save don't count. So since Asgore (and Flowey) are killed after you create a save, and when you reload a save it is before they are killed, their deaths don't count.

5) The exact circumstances haven't happened to me, but I've done the Asgore fight multiple times and seen those various bits of dialogue (often to figure out what happens because other people had questions about similar issues).