Building a Doppleganger

[q233]

So I'm playing a game where I've decided to be a class levelled doppleganger. Races of Destiny has a level progression for a normal doppleganger but MM2 has an Ethereal Doppleganger and I'm not sure how to build a full class progession for it. The standard has 4HD and CR 3, which comes out to 8 class levels, and the Ethereal has 20HD with a CR 15. I'm not sure if I should try and crunch the full race into 20 levels or try and follow the book's 'progession' and push it to approximately 35 levels. Either way I was hoping to stretch the abilities so that they're not all at once when they're gained, like slowly progressing the DR and fast healing. Any advice would be good.

[wizarddog]

The Ethereal Doppleganger is a 3.0 creature-as with all the monsters in MM2. You might need to convert its abilities to a 3.5 version before continuing. It might also have its CR lowered in the process.

Here is link to someone who did a savage progression for the monster: (It also includes the 3.5 update for the creature)

http://fallingstar.13.forumer.com/viewtopic.php?t=188


In my opinion, upon looking at the Ethereal Doppleganger, I find the monster utterly ridiculous. The powers it possesses are completely broken. If I was to recreate the creature, I would find powers that are similar in psionics or spells already in the rules.