I'm not sure. I haven't figured this one out yet. If I've used whatever it is I didn't notice.
I've played in moral dilemas - which I love with a passion.
I've played with using their own tricks against them, such as two sessions ago where they fought a spellcaster with the same spells as the party wizard.
I've tried whole session of nothing but shopping trips. They run around buying hotcakes and getting silly.
I've tried sessions of pure roleplay, they get into character and lead me around.
Hack sessions, they get out the bug spray and go to work.
I've given them monsters with no treasure, I've given them treasure with no monster (they got their first magic weapon last session - a +1 dagger, as a find on a dead body).
We have grappling almost every session, and every time we have to look it up again...
Sympathetic villains and heroes they can't stand.
Wisecracks and puns...
What I haven't yet managed is a TPK, or with this group - even a PC meeting it's end. Maybe that will do it...
I've come close to taking one or another of them out several times - one PC has gone down to negatives twice and been severely injured two more times, one, maybe two more have been close as well.
So I'm still searching...