Oh, by the way... as to your purpose being the destruction of the Good forces... I'd MUCH rather have it be the return of your hoard.
Why?
1) It's cooler that way.
2) Your CR is greater than 20... that's practically epic. You need an artifact-like weakness, me-thinks.
I will specify that it needs to be your SPECIFIC hoard, and every single peice of it. The money has already been spent, and it's going to be scattered across the globe.
However, the Lich King is USING that to keep a hold on you. He knows you can't be free until your hoard is returned, so it is in his best interests to keep your hoard scattered across the globe, making it nearly impossible for the good guys to get it back. And if they DO get it back, it means dedicating a LOT of resources... and besides, there's more potential for conflict right there... lich's forces preventing the return of your hoard, good forces trying to return it.
And of course, if they DON'T try returning it, you always reform a number of days later.
I have images of a certain pirate movie stuck in my head now... hehe.
You are under the effect of a suggestion that makes you THINK your purpose is the destruction of the good armies though, so YOU don't have to actively seek your gold. It's just that if the gold is returned, you go away.
Satisfactory?
Please note that in ghostly form, you can still gather up an army of your own (and will)... it's just that your baseline will be darn low at first. You've got a little ways to go.