3 Shadow Thieves, and 7 Cowled Wizards. 4 in the beginning, 3 at Spellhold.

Or maybe..

"Are you sure you wanna open this sarcophagus? It says something about a Lich.. And what about what those commoners told us"

"Nah, they're just lies. Everything those commoners told us was just vague rumors and suspicions. After all, they are just commoners.."

Probably not as get-to-the-point as the Dragon, but ah well..

<h1>Forget Spellhold, The ppl killed while our in your cage and the ppl killed where Imoen is taken</h1>

You just vetoed out your own post. Also, you said 'How many does he kill', meaning in all. You can't really verify how many he kills.
SPOILER>>
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>>At the end of the game, when Irenicus takes you to Hell with him, it depends on how many NPC's are with you, since they come along for the ride.

So in the end, you can't really answer.

From 12-17.

Huh? Aargh... let me make myself clear, or try to.

HOW MANY PEOPLE DO YOU SEE JON IRENICUS KILL FROM THE POINT IN TIME WHERE YOU ARE IN YOUR CELL UP TO WHEN IMOEN IS TAKEN AWAY