I had some trouble trying to get the triple exp bill to work for me while killing the zombie king in dark world 3-3 and no matter what I did it never worked for me. (

after a lot of experimentation I discovered that the triple-exp bill triggers on the VERY MOMENT ANYTHING GAINS ANY EXP. and you have to remember that casting any buff or any heal does give you some exp, however small. this completely wastes your triple-exp bill

that means it's only ever useful if you can kill whatever you want to kill in pretty much the first action of the battle, as even if the enemy team casts a buff or a heal or whatever, you lose the triple-exp effect.

I finally confirmed this by activating the triple-exp bill and entering into stage 1-1, kill an orc and measure the exp I got. it was 3 times the normal amount as expected.

BUT! if I first cast a simple buff like braveheart or shield wall and then immediately after kill the first mob, I only get the normal amount of exp!

skipping a turn and allowing the ghosts in that stage to cast their buff obviously has the same effect. it wastes your triple-exp bill.

so the reason it never worked when trying to kill the zombie king it was because I was slowly killing it with poison over many turns. using the "health" skill on a thief (which poisons enemies) grants about 100exp but with triple-exp active it gave me 300 exp. clearly it was wasted right away. abusing thieves is clearly broken in disgaea 2, but it seems built into the mechanics that you can't abuse them AND use triple exp to really boost in levels quickly from the start. a shame.