I'm playing both sides, so I always come out on top

Game Logic(TM). 

If you need to headcanon it, his Tome clearly gives him some Tzeentchian power, which allows him to advise every faction at once - hedging his bets to ensure he always wins.

So the different races in the campaign spare the advisor in their intro because he is necessary to reach the forge of souls.

But if that's the case... How come the other races can beat you to it and reach it as well ? Did he make multiple clones of himself like Naruto and is actually advising all the lords competing on the campaign ?

Something doesn't make sense in the Warhammer III campaign (spoilers)