In the Scourge of the Sword Coast adventure, one of the mini-bosses is a durzagon (a half-fiend duergar). I'm currently trying to update/reformat his playtest stats to be more in line with a proper 5e monster.
He's got most of the duergar abilities, except that he gets invisibility (as well as darkness and heat metal) as bonus racial spells (along with an extra 2nd level spell slot for each spell). I can easily just give him the 5e duergar's Invisibilty action and give him darkness and heat metal as 1/day each innate spells. Done.
He's got claw and beard attacks. The beard attack he can only use against a creature that he's hit with his claws. I can change this to a multiattack feature similar to what the grick has: he can make a claw attack, and if he hits, he can make a beard attack against the same target. Done. [EDIT: Oddly, I just noticed that the claws have a range of 20/60 ft despite being listed as a melee attack. I think that might be a mistake.]
Now, instead of the 5e duergar's Enlarge action, he has the following:
Reduction (1/rest). For 1 minute, or until he ends the effect or loses consciousness, Nalifarn reduces himself to 1 foot in height, reducing his gear to fit the new size. As part of the same action, Nalifarn can also disengage.
Anyone? Anyone? Bueller? 
I used the Durzagon as a major villain in 3.5E, but never got into 4E with any significance.
Personally, I would look back to its roots of being a half-duergar and half-fiend.
That means it keeps the enlarge feature like the duergar, and I would add the ability to cast darkness and include devils sight from its fiendish heritage.
I don't think reduction makes a lot of sense to me, and I see no justification for it. But, if I did use it, I would use it in combination with invisibility to escape through a small space. A villain escape tunnel of sorts I suppose, complete with trap to prevent pursuers.
If I wanted to increase its power, I would do things like change his invisibility to improved invisibility, and perhaps add other fiendish qualities.
Qzoo wrote: