I'm trying to present a routine to the theme of Lord of The Flies. Something about the inner evil of man or something like that. Any suggestions?

Have a million black flies emerge from your mouth (have you seen The Green Mile?).

How about Andrew Mayne's Gutbuster? You could grab an assistants black heart on the way thru and show it to the audience before putting it back.

I wouldn't do these at kids parties though

Place the names of the 7 deadly sins in 7 envelopes and 7 noble traits/ideas (Love, Peace..) in 7 more. Have 7 specs pick an envelope at random and open it - everyone's a sinner.

Use the conch as a prop in a jumbo shell and pea game where the conch always shows up wherever they pick.

This is a very interesting Idea, worthy of an incredible moment in magic. Perhaps a Gem turning black? Or, perhaps, when you add a black gem to a bunch of pure gems, they all turn black?