Is there a source to connect (mystically, or otherwise) those enemies of the Jews (presumably Amaleki) killed in Megillas Esther 9:12 with the 500 men from the tribe of Shimon who killed out the remainder of the Amaleki in Divrei Hayamim I 4:42-43?
The shiur that was referenced states that the reishish chochma says that Mordechia donned sak (sackcloth) which is gematria 400 to counteract Eisav (who attacks the Jews with 400 men). The sak leads to tzayis (listening) which is gematria 500. The magid shiur then pairs this with the pasuk (in ki sisa) kach lecha besamim mor dror (mordechai) chamesh meos (500). This all parallels the 500 people killed by the Jews in shushan.
He doesn't mention anything about Shimon and those 500 men but it would fit very well with what he was saying (someone should tell him). Especially because Shimon is related to shmiyah (listening)
Listen to this shiur which discusses this idea: http://www.filefactory.com/file/7gdq80su0oxb/n/Drasha_Purim_RCK_-Purim_2012_mp3